Having used Android iOS and WP8, here is my experience. maybe that helps you to decide if a switch is for you...
I started with iOS because it was cool at the time and to be honest, it does what it does pretty well. It is simple to use and there are TONS of applications out there.
What led me to leave iOS though was that the only way was Apple's way and the loyal fan base accepted everything without ever questioning. I vividly remember when Apple shipped the broken iPhone 4 (where you could kill every call by holding your phone and touching a spot on the metal frame) and instead of coming out saying "sorry, we messed up" the answer was: "you are holding it wrong" or " just get a cover". This behavior pretty much killed the iPhone for me.
I then switched to Android and to be honest I was pretty happy with it. I enjoyed the flexibility and the massive amount of applications. Over the time though, I realized that I really only use a handful of apps on a regular basis and that I was missing features in the OS that would make me so much more productive. On top of that, I started to experience many problems with freezing apps and randomly restarting phones. Since there really wasn't a lot of alternative I stuck to Android until last fall.
When I learned about WP8, I pretty much had the same concerns as you do. The apparent lack of major apps I used on a daily basis was quite a concern. But when looking at the OS more closely and realizing that it finally does what I was looking for to keep me productive (complete office integration, sharepoint integration, Lync on my phone....) I gave it a shot. From the fist day until now I have not once looked back to the other OS. WP8 simply does everything it does extremely well. Yes, there are some trade-offs like the lack of a notification center and some official apps missing in the store. But here is what I found out about myself: There is absolutely no reason to use an app to access a mobile site if you can just use the mobile site instead. Take facebook for instance. I get updates from the people I care about via their tiles and usually use the people hub to check on all the others. And beside that, I log in to facebook's mobile site every once in a while. I deleted the facebook app I had installed because I really never use it. I am sure that many of the sites you mentioned have decent mobile sites, so I believe a simple bookmark can do a lot for you.
As many others already mentioned, there are plenty of 3rd party apps out there, that work very well and often even better than the official apps. And truth to be told: Some apps will probably take a while before they find their way to WP8. This is the case with every new OS.
I think you need to ask yourself two simple question:
Does the best smartphone camera out there outweigh the fact that you might not have all the apps you want?
Are the apps you are missing really that important to you or are you just using an app for certain things because there happens to be one?
As I stated, I am not looking back because there really is nothing I miss.
And as for market share:
WP is here to stay, at least in my book. I come across many, many professionals every day and to be frank, most of them have no idea what my L920 is. But each and everyone of them asks me about it, plays with is and tell me that this seems so much better than what they have now. The more people come in touch with the OS, the more people will switch. So if you make the switch, it is up to you (and any of us) to help keeping WP around

I agree
Whatever your answer is, at the end of the day the phone has to work for you. It does for me, so I would highly recommend WP8.
Good luck with whatever you end up with!