I doubt it's any coincidence that Apple started relaxing their grip on the App Store with the release of the iOS AppleTV.
This is too many platforms and markets to leave vulnerable to competition by a more open solutions.
For example: BitTorrent for a TV device is a killer feature for me. Will AppleTV ever offer this or should I wait to see if Google TV will?
It's just a given that many people want a TV device that can acquire and play video from anywhere and in any format. Bittorrent would be a killer feature for me personally, that is all.
If AppleTV doesn't do this, the adoption rate will be lower. I think it's safe to say that AppleTV hasn't been a runaway success to date with the iTunes Store as the only source. The video sharing stuff in the new AppleTV indicates that Apple wants to open it up to more options. The question is how much farther can it go via 3rd party apps and it's exciting to think about.
But Roku or Boxee, as others have suggested, look a lot more attractive in their openness and integrated sources right now. A theoretically hackable Google/Android device seems quite tantalizing too. A fast VLC on the AppleTV sounds like a killer device just begging to download content too.
Specifically, it is just too cheap in comparison to the other devices that it is nearly identical to. Even the cost breakdowns of it are showing way too low margins from the raw parts (which were priced at almost $70). They really seem to be selling this product subsidized by iTunes and Netflix.
Therefore, an argument that "the adoption rate will be lower" seems kind of silly to me... about as weird as the people who claim "the (ads or paywall) on your website are causing you to lose readers": it doesn't matter how many people are using it, the question is whether it is making money.
So, if everyone in the world buys one because it supports getting moves for free via BitTorrent (are legal things distributed via BitTorrent? yes. more than two movies you'd ever want to watch? no. are you allowed to get a copy of House via BitTorrent if you pay for cable and hulu? no.) the product would be a complete failure: it would be more successful if no one owned it.