At the risk of invoking "oh not this shit again", it always bugged me how that Tarkin 720p/1080p comparison wasn't exactly apples-to-apples, with the colors not matching and I believe some image sharpening effects in there too.

So I made a gallery of a couple of other BD screencaps (fullscreen) at 1080p/720p/480p/240p so people could better visualize the loss of detail at each resolution, without getting distracted by changes not introduced by the scaling or re-encoding processes. I thought the results were interesting enough to share, although I think the Tarkin shot is still adequate for most purposes.

https://drive.google.com/file/d/0BxypVa35j2XsRHp4Z1hKcU04MWs/edit?usp=sharing

EDIT: To be clear, these results are very specific to the 2011 Star Wars Blu-rays. Different sources would show a different amount of detail, and would produce different results.