Cross-Platforming
Code-wise how simple is it to make a game in XNA that compiles on PC then compile it for 360? And how will devs be able to add or remove features between both WITHOUT needing to recode? are their methods in the framework that will allow me to execute certain code depending on the platform?
ex. Control scheme, obviously I can't play a game that requires a mouse on the 360, and I cant play a game that requires a controller on the PC. Or does XInput have actively configurable schemes availalbe?
"I cant play a game that requires a controller on the PC"
Actually you can. The wired 360 controller works just fine on the PC. I'm in the process of examing XAct and XInput now using the August SDK. I'm not sure how different it'll be from what's released but it can't hurt. 
Probably 95% of our APIs are the same across both platforms. The 5% that aren't are APIs that are usually considered advanced scenarios. I.e. I expect many, if not most, games to be able to share 100% of the code across platforms. You will need to create a project per platform and then add the same code and assets to both. "Porting" a Windows XNA Game to the Xbox 360 should be very easy.
