fondue: I think the copying-to-memory thing is so that:
scrubbing forward and back within the player is nice and quick, and when you present the movie (full screen, no interface) it can loop without hiccups. I use a 1997-vintage PowerMac and the delay is barely noticeable even on 75 mb movies. The QT player's volume control is surprisingly bad interface design, but it functions in normal sync with other system sound controls.
I've seen none of the other issues you mention on Macintoshes, so I suspect the problem is not in QuickTime but with Microsoft allowing Apple access to Windows APIs. (16-bit look, freezes, slow resizing, etc.)
Although it's no substitute for a professional editor like Premiere or Final Cut Pro, the QT Pro player does playback and basic cut/paste/scale/crop/export editing pretty well. And it looks as good as the compression on the movie it's playing allows.