On Windows 7 dwm.exe adjusted itself according to the application. On Windows 8 and 8.1 it does not. As a result you will often get poor performance when playing old games and even some new ones due to the incompatibility of the video mode or something or other. The bottom line is that it made Win 8 useless as a gaming system.
That's not it. In fact, Windows 7's "adjusting according to the application" is what caused the palette issues with 8-bit video modes. That doesn't happen in Windows 8.
The reason for the slow performance is that there seems to be some kind of DirectDraw emulation going on for DX7 and lower. It happens in games as recent as Unreal Tournament's D3D renderer, even. OpenGL renderers are unaffected. I think, using either certain AppCompatFlags in the registry or some option in aqrit's ddrwapper it can be disabled, but I'm not positive.
The downside is it makes <DX7 games run at about 20FPS across the board, the upside is being slow is actually good for certain troublesome games like Jedi Knight or Mechwarrior 3.
I'm going to see if this is still true for Windows 10. I suspect it to be.