The 10-15% incompatibility is way off, though (unless he is counting every single minor display variation resulting from IE's backwards implementation of parts of the DOM box model). Its not really Mozilla's or Opera's fault that there are still people out there that only design sites for IE bug sets and not standards. They try to accommodate the bugs and poor implementations for compatibility, but its a huge challenge. Luckily IE is slowly moving more towards standards compliance now. IE7 was a baby step; let's hope IE8 can pass the acid2 tests.
FF seems just as "fast" as IE to me on the machines I've run it on. Opera tends to be snappier, but he was comparing the speed to IE mostly. I'm not sure how many people actually believe FF is faster than Opera... just more "common myths" this guy has concocted for a longer article. Sure there are idiotic fanboys, but most people aren't at that level.