Since GW has no ongoing costs, it's not really possible to directly compare its success to WoW. All fine and dandy selling 5 million copies but if only 1 million of them are actually playing a month later its a whole different story. (Numbers made up of course)
On thing thats close to being certain is that GW2 alone will not be responsible for much (if any) drop in WoW subs simply because people will just keep WoW active while playing GW2 on the side, especially since the hardcore raiding crowd won't be satisifed in GW2 with its lack of PvE raids.
As for the patch date stuff, it's been fairly common for pre expansion patches to be roughly a month before the expansion, just a happy bonus for Blizzard marketing that it happens to be a competitors release date as well this time.
"Hardcore raiding" in MoP.
Thanks for that, my laugh of the day
![Big Grin :D :D](/styles/default/xenforo/vbSmilies/Normal/biggrin.gif)