I agree with you, I think it is the way you describe, men are just automatically entranced by extremely attractive women and only later realize that they may or may not lack other important qualities (intelligence, amiability).
As far as the other way around, why very attractive men aren't seen with mediocre females, I'm stumped. Honestly, (at least this is the way it goes for me) I find (usually, NOT always) extremely good looking men to be later classified in my "jerk" category. Many a time I find those men to be so arrogant and judgmental, perhaps due to the fact that they are being lavished with attention by so many women, that I really want nothing to do with them. It's gotten to the point that when I sit down with a group of men the first I "tune out" is the most attractive. Seriously, I automatically shut him out and (horrible as it may sound) unconsciously label him to be immature and snotty. I let the other girls fawn over him and get chummy with the "hottie" while I plop myself down next to Mr. mediocre and proceed to brain-pick. Maybe this is why so many good looking women are seen with so-so men, they've just "been there, done that". And by the way, do any of you other girls find yourselves doing the same thing I do?
I have seen the mystics play there,
Once or twice but I knew they had a reason.
Enchantment plays it's cards all right,
Hand in hand with the working of the seasons.