More specifically, "How Lake Wintergrasp will give War subscribers."
I used to not be a fan of PvP in MMO's. I know, you are shocked, but it is true. I grew up on single player RPG's and other single player games. When I got into MUD's and MUSH's, it was always for the role playing and other non-pvp content. When the graphical games came on the scene, I never really participated in their PvP either.
It wasn't until Lord of the Rings Online came out that I became a fan of PvP. I know that sounds strange, as LoTRO is mainly a PvE game. When I first started playing it, it was for the PvE content, but one day I thought I would try out their Monster versus Player PvP system. After that, I barely logged into my player character anymore.
I think Lake Wintergrasp will have the same effect on many WoW players as time goes on. World PvP that allows you to advance your character, has a goal and has familiar enemies is very addicting. Wintergrasp may not have all of these ingredients, but it is offering a taste of what non-battleground PvP can be like.
Once players get a taste they may find that they like it, a lot. I know I did, but I found that LoTRO's system just wasn't enough and it never would be. I went looking for a game dedicated to that type of gameplay and found WAR. The same is likely to happen with WoW, as it is a PvE game at its essence. There will never be enough to satisfy the player who wants to do Wintergrasp type activities with all of their gameplay.
Over time, I think the inclusion of Wintergrasp will actually send folks to WAR. Of course, it may be an insignificant amount, relative to WoW's base. This is one downside to WoW trying to give players everything they want, they just can't give enough.