While I can appreciate what you're saying JDonner, what you suggest is not at all simple. Drawspace consists of many different components, only some of which are provided by Invision (like the gallery module). However, by necessity, most of the site consists of software either provided by third parties or that we developed in-house. Each official patch released by Invision has a chance to break some functionality that these other pieces rely on, so we must test each patch thoroughly before making it live. (Even if we had gone with some other forum software -- like SMF -- from the beginning, we would still have these problems whenever the SMF team released a major update.) Keep in mind that SMF was still a very new and very much unproven product when work began on this iteration of Drawspace. We simply tried to make the best choice from the tools available at the time.
As for IPB 2.2, it turns out this update breaks just about everything.

As a result we need to wait on updates for our third party modules and write patches for our own code, both of which take time. Besides this, there have been a rash of security problems with the new code in IPB 2.2, so we're in no particular hurry to upgrade just yet anyway.
I'm also not aware of any new features in IPB 2.2 that would alleviate any of the spam problems we're facing. I believe that the measures we have put in place now will significantly reduce the amount of spam that makes it through on the forums (please keep reporting anything that does make it through!). The spammers may adapt eventually, but for now things should return to normal.
Over the long term, we are looking to migrate away from IPB (mostly due to poor support response times and security issues), but for now we're stuck with it.
Hopefully this sheds some light on our decision-making process.

--Warf