they didn't "make it ugly again"
those screenshots predate Aero. That's right before they dropped Plex and the GDI desktop compositor for their new engine.
The reason it's so ugly is they've got two generations of tech there. The big toolbar at the top with the title in it, is the thick toolbar you see inthe Aero screenshots, and right below it, is the classic Explorer toolbar.
As for the poor quality of the appearance theme, once the new renderer is active (as it is in all those Aero screenies) you've got a whole new world. It's like the difference in X11 (old hat, 2D, bitmapped) and Quartz (next-gen, OpenGL accelerated, PDF vector based).
it's something that Linux dudes should think about... why keep dicking around with tired old X11 when EVERYBODY ELSE is going to vector-based high-quality desktops?
<shameless plug>Get in on the Linux Next Gen Desktop project, and help build CthulOS. We've planned for the "Dagon" display-ghostscript layer, and an advanced NeXT-based architecture. Help us with the future, and we can actually make Linux better than Longhorn</shameless plug>