They can put them in the same iTunes store location as all of the Apple Lossless music tracks.
Even if Apple does sell "720p" shows, you can expect them to be so highly compressed that very few people would consider them to be HD.
How can you say that.
Apple today already offers "free" 1080p content. Where you might ask, look at the HD trailers on Apple.com. The quality of both 720p and 1080p there is excellent. The quality of those trailers played in full screen on my 30" ACD blows away watching a fullscreen DVD on the same system.
It seems that people forget that Apple was one of the first to offer 1080p content on the web (they may be the first) and they offer the most (granted that's based on nothing!). They are well aware of HD.
One of the complaints we've been hearing for years has been the lack of 5.1 support in Apple's DVD player, perhaps Leopard finally addresses this, which could explain the delay in TV.