I guess it just depends on how you want to define "demise" or decline, or slow moving death, I'm sure myspace saw the same small decline and attributed it to outside factors and didn't really do much to recapture the market.
I'm not privy to the inside details at the .com but 2 changes of ownership, tons of management turn around, more/better competitors in the market, I could see some reason to be concerned with vBulletin as a whole.
As for .org, its always the same, it comes and goes in cycles. The .org will probably far outlive the .com in some way or another.
But like others have said, forums in general are a dying breed any more, they've served their purpose, and are still great in limited topics, but for the most part I'm pretty sure their riding their plateau out now and probably wont be around in another 5-10 years.
Personally if I had anything worth .02 in the forum game, it'd be on the market right now to be gone