While the covers to most of your regular press books haven't been exactly my cup of tea (readingthedark's explanation seems likely), I will admit that they are all of a kind. I can see that they therefore might be more recognizable to a casual reader, as they look like they belong together, and each one is also likely to attract the same type of reader. I think it's a net positive - it indicates that there's some thought and even possibly long-term planning on Roc's part. I'd like to think that planning and forethought trumps clueless randomness...