Bear in mind that both pictures of Chelsea are unposed, using random available light. The other photo, of Pamela Anderson, is a studio shot, by a professional fashion photographer, under perfectly controlled lighting, after a lengthy make-up session by someone who makes up stars for photo shoots for a living. Of course Pam looks better.
And take a look at this:
Beautiful People with, and without, makeup and studio lighting.
Is Pam really prettier than Chelsea? Under the same conditions? Yes, probably, she's a very pretty woman. Chelsea's bone structure is out of fashion; round faces aren't considered exceptionally beautiful nowadays, although they were a hundred years ago. Look at illustrations in Dickens and Thackeray, for example. The fashion changed. It will change again.
But even so, it's unfair to compare posed, exquisitely lit and made-up stars to random women surprised by the paparazzi. I would guess that 9 out of 10 young women, if professionally photographed using all the tricks of the trade, would look damned good to most men.