...where to begin?... You see, one of the things that Android phones sorely lack is a proper integrated music/video service. iOS has iTunes, WP7 has Zune, Android has a mess. Sure, you can torrent stuff, use Double Twist, use Amazon MP3, etc. but it's a disjointed hassle. Now try using Zune. For £7.50 a month, you get all the music you can shake a stick at, and you get 10 songs to keep. To put that in perspective, those same 10 songs on iTunes would cost £7.90, and you'd get nothing extra. With Zune, I just download whole albums, listen to them as many times as I like, and if I decide after a while that I actually only like a few of the songs, I can bin the rest 'cos they didn't cost me anything to start with. And if I want more, I just go to the marketplace, and drag and drop a couple more albums onto the phone icon... It's that easy.
Secondly, as you should be aware by now, there is no fragmentation with WP7, and no waiting around while your manufacturer decides whether it is going to bother releasing the new OS upgrades to you. If you buy a WP7 phone, you know that it is going to have access to Microsoft's updates when they're released - because the manufacturer of a WP7 device doesn't need to customize the OS, whereas the Android manufacturer needs to add custom drivers etc. and do its own testing to make sure the update doesn't brick their phones.
Thirdly, when you buy Android, there is no minimum spec for manufacturers, which means that there are some very cheap Android phones out there, but also some very crappy ones (resistive touchscreens and 2mp cameras, etc). When you buy WP7, you know that the minimum spec is very decent (capacitive screen, 5mp camera, etc.). (incidentally, it is also possible to replace the built-in memory on a WP7 phone, it just requires a Torx screwdriver set... but hey, it's easier than trying to upgrade the memory on an iPhone...)
I could also go on about the advantages of xbox live integration, and the fact that the WP7 app ecosystem is waaaaay more advanced than Android was after 3 months, but I'll stop there, because you can see the point. There are just some things that WP7 does better than Android, and for some of us, those things are what matters.
Are there advantages that Android has over WP7? Of course (tethering, USB storage, etc. could be very handy). BUT, do those advantages outweigh the deficiencies of Android? Nope. A simple look at the stats will tell you that customer satisfaction ratings for each OS will tell you that WP7 users are a lot happier with their devices.