He's going to write his own renderer, he's not using SDL or anything. He's going to be opening his own windows and drawing to them directly. The chance at portability is extremely slim, and on top of that those of us who use saner operating systems won't get to enjoy it for a long time.
SO the portability effort is - opening a window and drawing? How is that difficult. Writing his own renderer means its pretty easy to be portable. He'd have to make a special effort to include platform code in what's normally a pure-math engine, right?
