Well me and my friends don't necessarily rate girls by numbers, but we do look at them and there are various things we do. "Hmm" vs. "Hmmmm" vs. "HMMMMM!" could be one. "Oh wow, look at her" could be another. We don't really have a standard method, just however we can get the point across.
And yes, guys do tend to create leagues and stuff like that. Honestly, anyone that is in or has been through high school (which should be all of us on this site) knows that high school is an extremely horrible place to get a good perception on the real world. What was it? Pretty people with pretty people. Popular people with popular people. The latest fashion could make or break a person. The things you say could make people like or hate you...then you graduate, look back, and realize how stupid all that crap was. But at that point, the damage is done and we are already used to seeing stereotypes be true. That's why "dating leagues" survive past high school, because we've seen nothing else but what we thought to be true.
Well I really am not good at ranking girls from 1 to 10 like people usually do around here...
But yes, guys really do categorize girls. They say "this girl is attractive, this one is not. this has a nice body but is not attractive, this has nice clothing and a nice appearance" etc. there are also other, personality-judgemental ranks as well.
Low means he doesn't really care about her, high means he cares about her a lot. :P