Judging by their use of chameleon, and their general UI choices, I think we can expect an iOS client from github as well in the future (using the same codebase as this desktop version). I think that OSX + iOS > Windows users in that regard.
We chose Chameleon because it provides for an awesome layer-backed environment to code AppKit in.
Everyone's all cuckoo about Chameleon because it lets you port iPhone apps — but the real win is a fully layer-backed environment with modern APIs (UIKit).
Our decision to use it has nothing to do with iOS at all.
I'd say the choice of Chameleon was driven by them wanting it to look "modern" or iOS-like. A native Git/Github client like this doesn't make sense on a device where you can't develop code (except in the web browser with Cloud9 or something).
In respect to the Windows question, I wouldn't be surprised to see them ship one in a few months, once they iron out the bugs and determine exactly which set of features a native client needs to provide.
