Actually it's the engine that has a hard time - I'm not sure how they draw the world - but I can tell ya it's the suck :P
Ever wonder why the lag in the bazaar is bad? It's not the number of people - look at the ground and everything is fine - data packets are not dragging your comp down.
The problem is when you look at a wall not only the wall is rendered - but everything behind the wall also.
Every *new* model also has separate models for the teeth, eyes and such - all the armor is *over* the skin of the model that is drawn every time you look at someone even though you can't see it.
*That* is why you need such a good system to run new models on.
The old models used skins that actually changed the skin of the model when you wore armor - that's why they were alot less laggy.
If they added the code - or fixed it - so when you *can't* see something it isn't drawn - everyone in EQ could play with all new models in the bazaar and never lag - even with an old geforce1.
The actuall polygons are not *that* detailed - it's the layer upon layer with the stuff drawn behind the walls that causes such grief.
Currently the only way to stop drawing stuff behind a wall is to narrow your clip plane down to where everything is in a fog.