Ug. And if it hasn't been beaten to death enough...
Half-life started on the Quake 1 engine. Valve ported some Quake 2-like features to the "Half-life engine" like individual palettized textures (Quake 1 had one palette for all textures), radiosity lighting (purely a compile tool upgrade, direct only is a still a compile tool option), and probably a few other minor things.
My theory is the visibility system was never upgraded, and thats why HL slows to a crawl when the world polygon count (commonly, r_speeds) goes above 800-1000, regardless of how powerful your computer is, but newer engines like Q3 can handle 2,000-10,000 world polygons and still run at 167fps.
As for the models, 8 moving counter-strike models brings my older Pentium3 700 system down to about 35fps, from 99fps. It will still bring my 1.33ghz Athlon system down to around 70. Say whatever you want about their models, they take a LOT of CPU power in numbers. And who says Valve is using the exact same code as other games with skeletal animation? Or that the Half-life engine can handle it well? I'm just pointing the finger, and I don't think I'm off base as far as what I'm choosing to blame. It's not trollop's system, because it happens on every other system I've ever seen play CS.