Alan, what definition of "Open" says that an open source product can't work with closed source products?
Without arguing Oracle versus PostgreSQL, I point out that some people like and trust the Oracle product. (Myself included. Disclaimer: I'm an Oracle-certified DBA.) As it is, OpenACS is pushing toward being "database neutral". I've never really believed in the attainability of database neutrality, but OpenACS is doing as good a job as I've seen yet.
A product like OpenACS that is restricted to a single database simply because the alternatives aren't "open" doesn't sound very open to me. (And, boy, would I be upset if Vim didn't run under Windows.)
