Goldy,
Maybe I'm missing something (well, I'm definately missing something, just don't know what) but it would seem to me that un-flat surfaces would lead to leakage and that that would prevent enough pressure from building up to blow out the gasket. On the other hand, like you and Erling are implying, how can it slip away at all if it is uniformly squeezed? I might slowly be coming around to your thinking, but I still don't like the bad fit.
Richard L.