yes it is human nature to want to talk about appearance. It's not always professional or polite to do so.
There's a large difference between commenting once that an athlete is shorter than their competitors vs. stating that an athlete looks like she should be playing with barbies and things like that multiple times. It's a matter of tact and emphasis.
If there was an albino runner, the commentator mentioning once that the skin condition creates some issues training in the sun vs. the commentator babbling "Look at his skin! It's like a ghost! Just look at it! Wow!"
Personally, I don't know if the first case needs to be said, but I'm not upset if the commenter says it. When I hear comments like the second, I think the commenter needs to be fired. "Playing with barbies" is much closer to the second." tact and emphasis.
Here's a clue. Only mention physical things if they are pertinent to the competition, and then keep the focus on how it affects the competition. Babbling on about physical appearance that has nothing to do with the sport is unprofessional and often just rude.