^Rare exceptions do not override the rule.
What defines a rare exception? The Doctor's regenerations have been all over the place. Otherwise we just have Jenny, Romana, The Master, River, and that one guy who was hanging with his next incarnation. Also, with the fob thing, how do we know what happens when they die in that state?
If the rule is a new body, how do you account for those who seem to be able to determine their new form? Romana chose to look exactly like Astra. The Time Lords offered the 2nd Doctor various choices. Who's to say that couldn't be the same one?