Sorry but I'm still not convinced. It's quite likely that an astonishing proportion of that 8,000 consists of mediocre copycat releases, downright horrible releases, pointless bedroom black metal projects, and then stuff that is probably decent (which, by the way, I wouldn't count as "worth hearing.") If you think stuff like Drudkh is good then of course I can see you thinking the latest atmospheric black metal jerk-off out of Uzbekistan is worth hearing, but I don't. I need a little bit more than mere numbers to be convinced.
edit: Now, if we're including demos in the mix, then I could see how the 500 figure might be reasonable. I was referring to albums. I simply cannot fathom there being 500 black metal albums that I ought to listen to.