Well, there are a few things to consider... so I'll do my best to explain.
The boomstick is a great weapon for the level, but there are certainly better ones by your level. The agility on the boomstick is nice, which is why you may be seeing a decrease if you're going to a weapon without any.
However, another thing to consider is your weapon skill. As an example, if you're going to a bow and you haven't used bows since level 25, your DPS is going to be lower because your weapon skill is much lower.
One last thing to consider is that the boomstick is REALLY fast, so that means small, soft hits frequently. With a slower weapon and higher top weapon damage, your specials will hit a lot harder (eg steady shot, arcane, etc). So... even if your tooltip DPS is a bit lower, it may, in fact, not be. What have you been using instead? That may help us more.
Edited, Nov 3rd 2007 3:18pm by ZulFrieze