As to why the fixed resolution, my guess is it’s reflective of MSFT’s desired positioning for WP as sitting in the middle of a Mobile OS spectrum; between iOS (totally locked-down, fully integrated hardware/software) and Android (completely open, fragmented hardware/software). In a sense, I guess that’s where Windows has always been, though with WP, it leans closer to the iOS side. Given that, having strict requirements, like that on screen resolution, go towards providing a consistent experience across devices (regardless of OEM) and ensuring all apps work and display the same on all devices, making development easier as well. The way I see it is you get iOS consistency and security (and some limitations) with the broad device/form-factor selection of Android (less the fragmentation); though, as evident by the resolution limitation, there are of course some compromises made with this approach.

Also, rumor has it [1] that these limitations are largely being relaxed with Windows Phone 8 (aka ‘Apollo’) and the OS will support 4 resolutions. I believe MSFT is holding an event to announce details on WP8 in a week or two.

[1] http://www.digitaltrends.com/mobile/windows-phone-8-details-...