As a WoW and War player this here are a number of facts you need to know:
1) WoW is about to have patch 3.02 go live (estimated to hit on the 15th).
2) On the 13th of November you get a whole new expansion to play with. Unless you were in the end game raiding Black Temple+, most of your gear will be replaced by the time you hit level 75.
3) WoW is a game about getting better equipment so with a month to go before you can get better equipment, why bother.
4) Summer happened and huge numbers of raiding guilds fell apart as apathy set in and waiting for the new expansion.
5) Blizzard didn't help themselves by allowing sites to 'mine' their Beta data and allow people to show you what you can get in a months time.
6) Warhammer hit at the right time and has given people 'something to do' while waiting, maybe even swap the game that they were going to play 247.
7) Warhammer free month ends on or around the 18th of this month.
Now on to my opinion. I held off from playing War for a bit. WoW is boring atm and it's difficult to get a raid going when people know that the gear is being replaced soon. So I started playing War two weeks after the initial release. I even joined the server that my WoW guild in WoW used.
The problem is, that I've come late to the party and War is all about your interaction with other players. (You can level without once doing a quest). Areas are empty. Public quests are unachievable (well the later phases) and up until recently, you could only join your racial RvR event.
Then there's the queues. If you login at 8pm, you can't get to your server for at least an hour. However the irony is that because the game needs a fully populated server to 'function' you don't want to be able to get on a server immediately at 8pm. This server will have a low population at other times and the Player vs Player elements will degrade badly.
Ironically I queue for War, then go play WoW for an hour.
So my current feeling is that I'm dropping Warhammer the moment WoW patch 3.02 comes out and I think there are a lot of people who are in the same boat.
What I do hope is that Blizzard look at Warhammer and take some of the ideas on board:
1) Public Quests
2) Queue for a BG from anywhere (which a Blizzard employee has already hinted at).
3) Siege weaponry that can kill players.
4) The ability not to be able to walk through mobs. (This would enable position strategies where tanks could create shield walls etc).
There are probably a lot more ideas.