E-mail uses push notifications, you make it sound like it's on a 30 minute polling interval but that's simply not the case - it's nearly instant, certainly every bit as fast as on Android. Twitter does the same thing. Just read the documentation
if you don't want to take my word for it. Using polling for any kind of instant messaging is not something you want to do since it's massively inefficient, much better to let the server tell you when there's something new to fetch.
As for porting, what you are describing is the same on every platform. You have an iOS app and want to port it to Android? Better brush up on those Java skills because your ObjC is worthless there. You can theoretically use C/C++ as a lowest common denominator between the two but almost nobody does that except possibly for some very core functionality and then you have to write a ton of platform-specific wrappers for the device-dependent stuff anyway. Oh and the UI, which is probably the most time-consuming single part of your app if you want to get it right.
I will give you this - being the minority platform, WP7 certainly stands more to lose from not sharing a common language with Android/iOS than the other way around. I don't really want
WP7 apps that are just least-effort ports of Android apps though, and if you're as concerned about battery life as you say then you should find the thought of porting over a big fat VM just to run a few more apps abhorrent. It's not like porting is that
hard, and unlike Android, WP7 is actually fun to code for. I've put one app on the market already and am working on a second. Never could muster up the energy to do that for Android, well not on my spare time anyway, there's just too much pomp and ceremony required to get anything done. I do code for Android at work though, since they're paying me well to put up with it.