Yeah, okay, Mobi is old. Really old. And they're not especially helpful to programmers and hackers, pretty much leaving them to their own devices. On the other hand, it has the benefit of being able to run on almost any platform imaginable, and already has readers for said platforms. Sometimes there's value to being "old."
For your purposes, you should still be able to do the job of converting... even if you have to make it a 2-step process and convert your DocBook to some other format (like Word DOC or HTML) that Mobipocket Creator, or some other established conversion software, can work from... right? Of was there something I'm missing in your post here (other than your obvious shock and indignation at Mobi)?
Glad you're trying out a Kindle... quite a few of us are experimenting with it, me getting my e-books onto Amazon, for instance. You'll have to let us know how well it reads the DocBook files (once you get them in there).