But does that really matter? I mean, since the game is so old, shouldn't 'modern' pcs easily handle the extra strain?
yes it does, these models are not as old as the game, and furthermore the graphics driver is not perfect. If you have ever played an emulator then you know that sometimes a machine that is perfectly capable of running a certain game can sometimes be held back by the software running it, making it unplayable.
For an example I can't run PS2 games with PCSX2 on my PC because even though my cpu and graphics hardware are much faster than a PS2's by far, the software was not originally designed to run on them, thus there are so many bugs and slow downs, I can't really run any PS2 at an acceptable level. Through the further development of PCSX2 however this is subject to change.
Trying to get new tech to run with old games is a tedious process, and until Aali's driver is perfectly refined or until QGears project is complete, the game will not actually run "as well" as your computer could potentially handle it. So if this model were running in a game designed for PC in the last couple years, then your right it wouldn't really be necessary. But for this particular game and the software running it, it can cause some major slowdowns, unless you own a decently beastly (expensive) machine, which not everyone does.
Not to mention I am sure the model was designed at a much bigger scale than it appears in game. More so than just as a courtesy to those of us with less than the most modern machines, it is usually held as a professional standard to make things as performance friendly as possible. It doesn't really matter if he left the polys or not, you won't be able to tell at such a small size. What you will notice however are the slow downs.