The list of apps they have I would say frankly are highly questionable as far as the top apps go. I haven't even heard of a lot of them. I used a Samsung Focus for almost 8 months last year and finally decided to switch back to Android until the apps I needed were available.
I just picked up a Nokia 920 this morning and was pretty bummed to see that almost all of the apps I use on a daily basis are still not present almost a year later :(
I really like the 920, seems to be a great phone but I'm not sure I can keep waiting for the apps to catch up and I think it's what's keeping more people from jumping in.
Before I get flamed I'll add I'm not looking for some exotic/niche app. These apps I use daily and they are not available currently in the Windows Phone store on the 920.
Flipboard/Google Currents, US Bank, Sonos controller, Our Groceries (Serious waf issue on this one), dropbox (I know it's coming but that doesn't help me now and serious waf again as my wife and I share photos via my dropbox account)..