Where does there always have to be speculation, from completely uninformed people?
From my little knowledge of Alan Cox, from mailing lists, he always seems like the kind of guy who likes the lower-level details, and I imagine that few companies will be more interested in tweaking and improving the low levels than Intel. If they saw his obvious talent, and offered him a better job at better pay, then why not move?
Alan Cox leaving Redhat doesn't have to say anything bad about them, maybe it says something good about Intel, and the things they are getting more involved in?