They would, if it had success.
See, if a game manages to draw anywhere from 1 - 12 hours of gameplay per day from a rather large crowd (We're talking millions of people here), that seems to indicate to me that - Gasp, somebody must be having fun!
Its the most successful MMORPG, ever. Now whether that has something to do with timing, latching onto its existing customer base from Battle.Net, utilizing a well-known storyarc / game to bolster its popularity, plain rock-solid advertisement or the actual game itself is irrelevant:
Millions of people play the game daily. That is success, gentlemen. And while I can point out many issues I have with WoW (note that I don't play the game anymore, but I did for 3 years), I can also point out dozens of very, very good ideas.
The curse of copying something very, very closely is of course that if you don't do it better than the game you're copying - You're going to look like a cheap rip-off and its going to be a negative not a positive. One example of this is the interface in Warhammer Online, which is clearly jacked piece-by-piece from WoW but is comparably unresponsive and sluggish. *Bad* idea. Coincidentally, this is one of the most voiced complaints about the game (Sluggish responsiveness from the UI).
"Bah, they work too much on WoW and forget about the REAL games."
"I hope Diablo III puts WoW into a corner, PERMANENTLY."
I think you just hate World of Warcraft.