They definitely don’t always do this though. I mentioned elsewhere on here about a recent flight from LPA to LHR with 12 rows of CE, crew served starting at row 1 and row 12 concurrently so the middle of the cabin was served last. This weekend flying ARN to LHR with 12 rows of CE the crew served from row 1 and row 6 at the same time. It seems that the only way to guarantee a choice (usually!) is to sit at the front.