Does nobody remember how much slower OS X was with its own new flashy UI? It's not a uniquely Microsoft disease. It's the disease of thinking (and unfortunately perhaps they're right) that it's flashy visuals and a shiny candy look that sells an OS, not baseline features, performance and stability. I would guess that at least 50% of the reason for Vista's higher system requirements comes down to visual or other aesthetic "enhancements", not new features. Personally I was happiest with Win2k's clean look and solid performance. In XP I usually just switch to the 2K-like theme. With Vista you actually lose some capability doing that I believe.
Anyway I'm not saying you need to take up lots of resources just to have a nice-looking desktop. But the major players still seem to be caught in doing that, including Apple. I hear OS X can still be laggy for certain visual effects except on the best of new machines. Perhaps we just don't know all that's involved in doing that level of visuals across the whole OS. But I for one would much rather see time and resources put into other areas. We'd have more feature-full, more stable, better overall OS's that ran faster with less resources if there was less emphasis on visuals, fancy transition effects, etc.
- Oshyan