I'm not too sure about the different wireless standards, but I see the most expensive option is the a/b/g/n adaptor. With this are you just paying for the ability to connect to a networks?
Just did a bit more research and now understand that it's the 2x2 bandwidth that you're paying for.
The only thing that's stopping me buying now is the trackpad issue. I don't want to have to rely on a mouse, and I know I won't get on with that nipple thing! It's a real shame because, otherwise, it seems ideal!