well, seeing as I use the flisk model, I don't think that's the problem. Not every player I see is a sarge... but many of them are. When people use skins/models I don't have, it shows up as sarge... unless that many people are actually using sarge, I'm assuming many of them have custom pk3's in their baseq3.
Kitty used to play as the same model as you, but she's not around so much anymore. Player models don't really have an impact on the popularity of a server, but can be used to your advantage, some models blend better with some maps than others etc, Sarge is, generally, pretty easy to see so just shoot them all!