There's no question that WoW's population has slowed down lately -- the last time we heard an official update from Blizzard was way back in January, and while this analyst claims there are more nowadays, there's no question that things have plateaued for the moment. But maybe there are some more folks out there who haven't played yet, and maybe Wrath of the Lich King will bring them into the fold.
He also mentions Warhammer Online, as you might expect (isn't that pretty much a requirement anytime you talk about MMO populations these days?), but he's landed on the same conclusion both Blizzard, Mythic, and all of their players have already ended up at: WAR isn't really going to affect what WoW does, and vice versa. "Core WoW users," apparently, have "limited interest" in the other big MMO out there at the moment.