Well, the simple answer to your question is that the graphic artists and design geeks of the world tend to be Apple users. :-)

Yeah well, they've had Apple laptops and desktops for a looong time now and I haven't seen wallpaper this cool! What gives?

It's the combination of increased compatibility between Macs and PCs, as well of the improved market presence of both Macs as well iPods and iPhones. This stuff has always been out there, it's just now the PC people are more aware of it, or less able to scoff it off as a niche thing from "those crazy Apple people."

After all didn't you have an awesome wallpaper on your old neon-orange iBook? :-)