I agree with you, but I don't think most of those things are really vital for a great text editor. For the most part, it's just a giant window with your text in it, maybe a sidebar or two. Most of the magic happens under the hood. That's why I think this is a good idea.

Dunno about cross-platform app development, but Cocoa on OSX is pretty nice. QT isn't bad either, from what I've tried.