I think another large roadblock in higher quality movie content in iTunes is the iPod itself. HD movies will not play on an iPod, and so will sort of limit the content to at-home usage. In order for the movies to be at all worth buying, they have to be playable on the iPod as well. Video conversion software is no good as a work around since DRM prevents them from being altered in any way. If iTunes went HD, they pretty much abandon the iPod. It wouldn't seem very worth it to repurchase iPod compatible movies on top of the higher end stuff.