One C# game to rule them all(iOS, Android, WP7, W7, Mac OS X and XBOX)

Hey, I'm learning C# and just thought of a cool idea. Considering that a game was simple enough. Say, a remake of a classic text-entry style game, a C# game could theoretically be ported to all of the platforms I listed above, with little to no change of the original source code, correct?

Obviously the UI would have to be tweaked, and I highly doubt such a game would really survive on each of those platforms!

But, although C# is really MS heavy, through different methods, that could work, right? Or, would I have to change the C# source to Objective-C? Does Android even have an official language that they support like Apple and MS do?

This is kind of an odd question, but if this is true, then C# is really a nice all-purpose language even though it's largely based on and endorsed by MS.