Looks don't last though - so what will sustain the relationship once that's gone?
Probably you're right that a man will fall for a very pretty woman regardless of personality (even if she screams obscenities at him over trivia and isn't keen on sex?) But such a relationship will need something more if it will go the distance. On the other hand personality is surely a big plus that can make up somewhat for lack of physical attractiveness.
Science has shown that people naturally pair up with someone who is on about the same level of physical attractiveness as they are. Otherwise what would happen is that the less attractive people would always be disappointed.
You can get a beautiful woman who never gets married because she is flawed in her personality, while a much plainer woman who is a pleasure to be with, (and a good cook most likely) will have no problem.
I would agree with this.
I think the physical attraction will bring people together, but their communication will keep them together. The older I get, the more I realize that looks play a smaller role in choosing a mate, at least for the long term.
The longer you are in a relationship with someone, the more it becomes about the bonding one has created through conversation and experience than it does regarding the physical attraction which brought you two together in the first place.