Fair enough. But the IP also includes setting, characters, monsters, story, etc etc... It is a bit of an unfair comparison. An IP is a big thing.
I would say the IP will keep people there as well, probably more so, but again, it is an unfair comparison. I know none of the other features would matter to me at all if this wasn't a TES game. I simply wouldn't bother. The TES IP has kept me interested this entire time, nothing else has. I like the other features and they will help keep me in the game though. I have no idea how representative that will be though.
In any case, every feature is important, how important it is to the majority is hard to really say. I would say the IP is more important than the RvR concept, but that doesn't mean that RvR concept is in anyway unimportant.