GalleyCat appears to be interested in science fiction book covers because they have another item on the subject, this time a comparison of British and American versions of the covers for Charles Stross's Halting State and Ken McLeod's The Execution Channel. In the case of the McLeod book, GalleyCat finds a parallel between the near-future "accessible" science fiction of the story and the more-thriller-than-science-fiction covers in both the US and the UK. The Stross book, on the other hand, got a much more impish, gaming-oriented cover in the UK but a "digitized high-fantasy look" in the US, where the publisher seemed more interested in matching the tone of Stross' other books.
What is it about book covers that fascinates us so that we're compelled to analyze them? Perhaps it's because we realize it is so often the cover that makes us pick the book up in the first place.
Not a fun thought for a writer, but still likely to be true,