Apple has started loading the iTunes Store with higher-quality, 1080p versions of movies, and despite the fact that they're nearly 1/10th the size of their Blu-Ray counterparts, Ars Technica found that the quality is almost as good. Sharpness and colour reproduction were just about on par, though iTunes lost a bit of detail in grainy shots and had lots of issues with dark gradients (at least in the one movie they tested).
In the image above, iTunes is on the left, while Blu-Ray is on the right. You can see that a very tiny amount of detail is missing in the iTunes version, particularly in the lighter areas of the face -- hard to notice as it may be.
Still, for 1/10th the size, that's not bad at all -- plus you don't have to do the work of ripping it yourself. The one other big difference is that Blu-Ray discs contain a channel of DTS-HD audio, which is higher quality than iTunes' Dolby Digital 5.1 and stereo AAC tracks, so if you're an audiophile, Blu-Ray gets another point in that category as well.
Hit the link to see the full rundown, complete with many more comparison shots.
1080p video smackdown: iTunes vs. Blu-ray [Ars Technica]