I think the fear is that Microsoft would give up on WP similar to the Kin or Zune because of the low market share. Kin was a half-baked smartphone. It never stood a chance with its pricing and the fact that it required a smartphone plan. WP was already in the works by the time Kin came out and it didn't make sense to keep Kin. Also by the time WP was released, it didn't make sense to continue Zune because the iPod was already losing steam and the iPhone was catching on faster than expected. Basically WP 7 was the replacement for Zune.
Microsoft has put in a significant amount time and money in WP and has made it part of its overall Windows strategy as evidenced in converting to the NT kernel and now making Threshold. I don't see WP going anywhere anytime soon. It will be available in some form or another as Microsoft can't afford to lose the entire market to mobile devices that run iOS or Android. If they kill WP, Windows itself could eventually die. After all, we are in the 'post-PC era' and the last thing Microsoft is going to let happen is kill Windows. Anyway, just my observation.
Now to answer your original question, I'm interested in supporting Microsoft software and services. I'm sure they will be available in some form or another in the highly unlikely event that phones running Windows or WP are discontinued. I don't wish to support Android because I don't want to be tied to Google so if I can use Microsoft services on either, then I'm going to choose iOS.