I'm surprised no one has mentioned this yet. I think the reference in the OP is WotC's nod that the older versions of D&D are still being played and still have quite large followings.
Check out the Dragonsfoot forum. Tons of people there playing all the pre-3E editions, all the way back to the three little books TSR first published.
Plus, there are new products being published by niche companies all the time for earlier editions--not to mention the older edition rule clones that can be purchased (OSRIC is a good example).
If your favorite D&D edition is, say, 1E AD&D, there are a ton of people still playing that version of the rules, and you can still buy new products for the game (not near as much as you can buy for 3E or 4E, mind you). And, there's a ton of fan material on the net, too, from supplements to game worlds to adventures.