Why? Well, for the challenge first. Having a DVD drive most of the time doesn't mean it's the only one to target. Some even have no removable drives (by choice I suppose). Having to burn a DVD for only 1 Gig doesn't make me want to go for it. Or make it 4 Gigs and I'll be happy!
Unless this is for testing monster machines that already are unaffordable to most people -- you know, like «who's got the biggest...»
I don't know... Since PTS has testing profiles, why not categorize? Like profiles for CPU/memory/disk benchmarking only, video, 3D/2D, whatever. Amongst these profile sets, there must be which don't necessarily require that lot of resources, right? Also is Gnome absolutely unavoidable? Or is a lighter desktop also possible? Like XFCE, LXDE... I think there should be many ways to fine-tune the size and requirements of a PTS distribution.