Oh I like the idea of Hartnell being the first incarnation, too. (I did say I'd "almost" buy that!)
All they really need is a single line saying, "With the Time Lords gone, that limitation doesn't apply anymore."
RTD said as much (on one of the DVD extra features IIRC), and even expressed mild surprise that so many fans seem to put so much stock in it. OTOH, it could explain all those images of previous incarnations in... "Brain of Morbius" was it?
CHAP ("Completely Half-A**ed Theory"):
I've never minded that the Sixth Doctor looked like Maxil, and Romana II looked like Princess Astra. I kind of like the idea that some part of a Time Lord's (or Time Lady's) subconcious keeps a little mental Rolodex of faces it sees and might want to "use" in a future regeneration. If that's the case, I can write off all those faces in Morbius as, not actual previous lives, but just Morbius flipping through the Doctor's Rolodex.
My rationale is that we don't know how long he lived on Gallifrey before he left it. It may be that the First Doctor is the only incarnation to have anything like the length of life that a Time Lord incarnation usually lasts.