I don't think it's necessarily a bad thing to know what a pram is when you see it. As pps have said, when you're shopping around for a pram, obviously you're going to know which is which.
I put a lot of thought into which double I was going to get, so of course when I see an iCandy, Bugaboo, P&T etc...I'm going to know what it is.
As for judging, I don't judge the people, but sometimes the prams. When I see a strider plus, for example, I'll think "that looks so wide at the back, I wouldn't like to have one child underneath like that" those kinds of things...as for the people pushing them, I don't give them a second thought.