I think the question is about entertainment (e.g., movies, etc.). I don't know what you mean by "highly available on Macs" as I know of no providers for such content, other than 1080p trailers from the Apple web site. And those aren't too entertaining.
It means that there is plenty of content in HD and it is available on Mac's. I personally get over-the-air HD from local stations (18 stations - 10 of which are true HD vs just digital), Vuse, recorded work (FCS), Hulu offers 420p (weak, but still counts), HD content via torrents (mostly TV shows in HD via component not HDMI - but still way over SD), external blu-ray w/ bootcamp & XP/Vista and there are online shows shot in HD as well (Sanctuary is one example).
I am currenlty beta testing two online HD video packages for some popular companies and I'm pretty impressed. Right now I have a 10Mb (not MB) connection and it is being put through it's paces. There's no way you can get true full HD from the Internet. Heck, you cannot even get true HD from cable or satalite - they compress it so much! I also have seen Apple's HD player being tested so blu-ray is right over the horizon (probably this year).
Edit: I should have said HD not 1080p 



