but don't the new Macs use integrated GFX hardware as well as the low-end PC's?
Mac drivers for integrated (Intel) chipsets don't suck. This is a great situation if your projected development time is four or five years, but in the immediate future there are going to be a lot of these underpowered machines knocking about.
Vista is going to kill them off a lot quicker than you think. It'd be a bizarre paradigm shift in the BRL philosophy that would see them left behind. :/
BRL philosophy has always been to provide state-of-the-art technology. Five years ago, when Blitz3D was released it too required comparatively high-end graphics card. Just because the world has moved on in the mean time, doesn't suggest a paradigm and/or philosophical shift as far as I can tell. This means Shader support and usage of Shader 2 which is standard today.
Standard? Set by who? Since the two market leaders (AMD and nVidia) no longer produce cards that don't have SM3.0 and by the time Max3D is released, chances are you won't be able to buy them off-the-shelf either. Don't know, I played quite some game with dynamic light effects on my old 1,5Ghz P-M notebook with mobile radeon 9700 and it didn't have any problem after all.
You ran DOOM3 on that hardware without any problems? At what resolution, and detail setting, because as far as I can tell it only barely meets the minimum requirements, never mind what they reccomend. Hell I played FEAR on my laptop and had to reduce the detail and resolution significantly to get a decent frame rate. While they support Shader 3 it would be the far more intelligent decision to use the CPU as those shader units are totally underscaled for such stuff.
Even if that where true (which it isn't) it's not possible to simplify it like that. There is simply not enough bandwidth available to send per pixel lighting information of any decent resolution along the north bridge 60 times a second.