I used an iPhone for 2 years before getting my Windows Phone, so I had a large number of apps on it I really enjoyed. Therefore, when I got my Windows Phone, I also got an iPod Touch so that I could continue using those apps.
I love how my Windows Phone aggregates social networks, works across people, etc. but none of that is so much better IMO that it's worth getting the short shrift of every new app and game that comes out.
It's not just "Windows Phone needs <x> app and then I'll be set", because it's about future stuff too. It's not just apps and games I'm currently playing on my iPod Touch, it's whatever new apps and games that come out that I'd end up having to wait for.
Also, the one thing I use my iPod Touch for more than anything else is listening to podcasts. I love podcasts and audiobooks, listen to them all the time. Windows Phone still doesn't even have 1.5x/2x playback which I use exclusively on my iPod Touch. Now I've discovered iCatcher for iOS and the deal is sealed even further.
Then there's the apps and games that I do use for Windows Phone. NextGen Reader and Rowi are great Google Reader and Twitter apps for Windows Phone. But we're nearly a year after the release of Mango, and even these best-ever Reader and Twitter apps don't hold a candle to apps like Byline on iOS, in the state they were in two years ago. It's the fault of the platform and its reliance on Silverlight inhibiting developers from creating quality apps.
There is plenty that Windows Phone does far better than iOS, and WP8 enabling native code will hopefully go a long way toward improving the app and game situation. I'm just not sure the platform will ever hit the critical mass necessary to make developers care, so that leaves a whole lot that I personally use that iOS might always do better.