Who knows why it takes as long as it does. I think in essence, though, that's right--most of the time it just sits around waiting its turn and then, provided it's all straightforward, it get's processed in an hour or two by the ECO.
It is a shame that it's taking so much longer than expected, though. I wonder if the changing political situation in the world is somehow meaning they have a much longer backlog than they have in the past when it's taken about a week at this time of the year.