I agree also. Francisco clearly has a vested interest in this opinion, and like you say he's absolutely right about implementation making the difference.

I have given a Cappuccino app to people to use, and they didn't even realise there was a difference from the native controls (after the widgets rendered - which DID throw them).

Even though I fundamentally agree that re-implementing UIs from scratch is not optimal, Cappuccino had a valid reason for doing so, and its implementation doesn't harm usability.