Well, I didn't initially want to answer this because I'm not familiar with this application; however, in general, (from what I've read) for a programmer to manage memory usage is time consuming (if not difficult), and therefore memory usage is not always written into programs the way it should be.
So, you end up with programs that would seem to do relatively little from a user or administrator point of view, but which still take up a lot of resources. Just google "programming for memory usage" and you'll find plenty of articles that discuss this.