You can't argue with the math. Your graphics card has a limited amount of vram. When people are running around with 300mb+ avatars, they're eating away at that. You've also got the vertex data, the world itself, and so on. 
Having a couple of extra meshes or being over the 70k tri limit isn't a big deal, but having a bunch of avatars in a world with massive vram footprints will cause issues for people with even the top of the line graphics cards.