Must not be a dealbreaker for those on T-mobile, the lumia 710 moved up to #3 this week in best buy sales and #2 on T-mo sales. I also can't stand seeing when apps are for Android and iOS but not WP. I don't think WP will die because of it, especially since MS and Nokia will be pushing hard to get these apps.
You're really sort of spinning it, a bit too hard, IMO.
T-Mobile has like 10 Android phones that are equal or better spec than the Lumia 710 that all compete with each other, so it's not hard for one of only two decent Mango phones to reach the #3 spot, especially when it's almost free (if not free) on contract and those Android phones are like $199-249 on contract. That really displays just how competitive OEMs and Carriers have to be to push this platform at the moment. WP7 world-wide marketshare is very low, and even their US marketshare is very low.
T-Mobile is bleeding customers like never before, has probably the highest churn rate in the US smartphone market, and even has the worst Windows Phones available in this country (AT&T has the best, but they are overpriced when pitted against competing Android/iOS devices IMO). AT&T and Verizon have almost twice the customers of T-Mobile (if not more than that) so the Lumia 710, a free on contract phone, reaching #3 on their sales charts when 80%+ of their smartphone customers have Android smartphones says literally nothing at all. It's spin material, IMO.
The market exists outside of T-Mobile USA, and on both Verizon and Sprint WP7 is an afterthought. The iPhone 3GS is outselling most WP7 devices (if not all) on AT&T nevermind the 4 or 4S, and they have a ton of high end Android phones (so much redundancy there, IMO). Worldwide marketshare for WP7 is below 2%. It's a terrible economic decision to put that many resources into developing for the platform at the moment, because it really doens't seem to have much momentum *right now* despite how desperately the tech media and fansites are trying to push it in people's faces.
It's like complaining that Adobe doesn't port Photoshop to Linux, which is actually doing better in the desktop OS market than WP7 is doing in the smartphone market right now.
Total Android sales on T-Mobile still blow WP7 out of the water, and T-Mobile has stated that a huge majority (probably over 80%, though I'm accounting for time and being generous since then, because I'm fairly sure they said something near 90%) of their smartphone customers have Android phones. All of T-Mobile's high end phones are Android, and coincidentally they do not have issues running Zynga's addictive games and you can play Angry Birds for free if you don't mind the Ads.
Die is a bit of a radical term, since things don't really die, they just sort of fade out of relevance leading to consumers not considering them as an option. The lack of those apps suppresses adoption of the platform and really puts it out of consideration to a wide audience of potential customers. App numbers are market fodder with the way they're thrown around these days, but having a very high app count increases the likelyhood that your platform will have everything that a wider variety of users will need, and at a higher quality since competition for users in that ecosystem will be much higher (you won't be able to get away with putting out crap like Board Express or IM+ because you simply won't sale to many users due to better alternatives existing).