While what has been said here is true from a tech-savvy point of view but I'd like to raise a few more issues from two very different perspectives: average John & Jane Doe not arguing the pros and cons of a specific mobile platform with complete strangers on the internet on one hand, and the enterprise on the other.
Let's start with John & Jane Doe.
First of all it's marketing or rather the noticeable lack thereof. And that's not US exclusive it's true in all markets worldwide. A marketing campaign always needs to address two things: first of all raise awareness of ones existence and second create an image of your brand/product. Don't provide too much information, that's too confusing for most people. Be vague, creative and try to lure people into your realm of reality distortion. Apple has perfected this to the point where they don't really need to advertise anymore - everybody plus their grandmother know Apple is supercalifragilisticexpialidocious cool and they make the products to desire. Android on the other hand is carried by mouth to ear propaganda - if 90% of your friends use Android phones chances are you'll get sucked into it. Not sure about the US (haven't been there in a while) but Samsung does run massive marketing campaigns in Europe trying to create an image as 'the other Apple', like Apple's younger brother that is way cooler. They're not as effective as Apple by any means but it does work. Sony, LG, etc. do the bare minimum to advertise their phones but they are barely visible. Nokia I have yet to notice, they're practically invisible.
Second, not only do I think that the app gap doesn't matter but I am convinced that while it most certainly exists it's a non-issue to most people. In my circle of friends apps are not what matters, it's what people can or want to afford (see marketing) as long as it runs Facebook, Whatsapp, and maybe a game or two. Most people I know have less than 20 third party apps installed on their devices and use less than 10 on a regular basis simply because they don't care. Even Twitter, Instagram or Snapchat is something most people don't use - it's the tech savvy people that live and breath on the internet that do but that's a minority still. Most people are neither tech savvy nor do they work anywhere near the technology field. The problem with the internet is that only people who are on the internet can participate in discussions and quite frankly, 99% of all users out there don't give a **** about news regarding Windows Phone, Android, iOS, Blackberry OS, etc. Much like I don't really care about the latest inventions in hammers, lawn mowers, or floor tiling. I'm sure there are huge differences between the different brands and products but if I need a lawn mower I'll just purchase one that is availble at the store, period. Forums such as these are heavily tilted towards heavy users for whom the smartphone is an extension of the personal self but let's be honest: that's not how most people use their devices. I have a prime specimen at home - my wife. When the iPhone 5 was first introduced she decided she MUST have one, after having previously used an older 3GS that I had lying around at work and didn't need anymore. We spent 700? on it hoping that she might start using it (at least it would've been money well spent) but did that happen? No. Does she need a smartphone? Not really. Not once in her life has she installed an app herself, every third party app on that phone was recommended and installed by me. She doesn't even know how to do that, she has no idea what an AppleID Is and what an AppStore is. Does she use these third party apps at all? Not really, she simply doesn't see the point. Even the ones that I personally think are worth using, such as news readers. I'd say roughly 70% of her smartphone use is browsing the web reading gossip stories about celebreties and their ill-bred misbehaving offspring, 20% is texting, and 10% is Facebook. Occasionally she uses Google Maps to find out how to get from A to B and once every couple of weeks does she launch our local public transport provider's app to check the train/bus schedule to get home late at night.
Now for the enterprise perspective. As we all know enterprise doesn't care for coolness, Facebook/Twitter/Snapchat app availability or initial purchase price. It's the total cost of ownership (TCO) that drives decisions and as the head of IT operations for a large multinational corporation with more than 3,000 employees and one of three people calling shots in terms of mobile devices I consider myself apt to speak for corporations big and small. We went with Apple many years ago because back then it was the only device to offer full support for Microsoft's ActiveSync Exchange protocol and this hasn't changed to this very day. Google has ditched support for ActiveSync Exchange completely in favor of IMAP/CardDAV/CalDAV which, quite frankly, wasn't a huge loss because their implementation at one point even managed to crash our Exchange server. Blackberry went a different route and requires a Blackberry Enterprise Server and while Windows Phone does have ActiveSync Exchange support built-in it's incomplete and lacks certain critical features, such as support for public contacts. Another issue is device management and quite frankly once again there are only two competitors in this field: Blackberry and Apple. Managing hundreds or thousands of Android or Windows Phone devices is a major PITA because there is no management software available for central management. I am currently using a Windows Phone device to see if at some point in the near future we might switch from iOS to Windows Phone but quite frankly I don't see this happening yet. Microsoft has become a major player in business mostly due to their ActiveDirectory capabilities - I'm talking centralized software deployment and management, centralized update distribution, OS lockdown, etc. None of this is available on Windows Phone. Zero. Nada. A third issue is OS uniformity - only with Apple can you make sure all your devices are running the exact same operating system, even down to the minor version. Google's Nexus would be a competitor here as well but have already fallen back due to lack of ActiveSync Exchange support. Apple has one mobile operating system available for all their devices. I've lost cound how many different implementations of Android Samsung is sporting right now, and even Nokia doesn't run the same version of Windows Phone on their current lineup, it's a mess really.
There's a reason why most large companies use Apple devices and the reason is not because they're cool, super awesome and have the best selfie camera or narcissism enhancement app available. It's because while initial pricing may be higher than average TCO is much lower due to enterprise manageability. Imagine installing an app, modifying a policy or installing an update on 1,000 devices spread all over Europe running a plethora of different operating systems without a way of doing this remotely over-the-air through some sort of management service.
In short, this is also why Macs are practically non-existent in enterprise environments besides a few exceptions here and there, mostly for CEOs or upper management. It's all about manageability.