I don't see the logic of saying that two cases that are described differently should be treated the same 'in the absence of any further information to the contrary'. The different description is evidence to the contrary. It's clearly stated that downed crew fall off. There's no such statement regarding drivers, which surely suggests that they don't. If they were intended to do so then presumably that statement would be repeated.Seeing as people seem to agree that downed models get thrown off the vehicle, I feel that the driver should be included in this in the absence of any further information to the contrary.
Of course, it's not explicitly stated that drivers don't fall off, but lots of things aren't explicitly stated, e.g. nothing says that my Nob can't order an orbital barrage. There's no need for anything saying I can't, because there's nothing that says I can. Similarly, there's no need for anything saying that drivers don't fall off, because there's nothing that says they do. (This is assuming, of course, that I've not missed anything here - but you're not suggesting that I have.)
As @Azzabat demonstrates, you can house-rule whatever you like, but this thread is for questions about the rules, not suggested house rules. Adding things to the rules just because the rules as written don't have anything to the contrary, is house-ruling it, rather than interpreting the rules.