My contention is is that most people that play MMOs are neither. The raiders are by far the most vocal segment of the PVe population. By contrast, RPers barely even make a dent in their numbers.
But then there are people who play MMOs as if they're single player games, and they, believe it or not, account for a much higher percentage than anyone had previously realized. The first thing that led me to think about this was something Scott Hartman, lead developer for Rift said (and I'm paraphrasing here). He said something to the effect of MMOs that ignore solo players are likely to go out of business in short order.
A short time later I noticed in the Guild Wars 2 FAQ a question about can I solo Guild Wars 2? See, they didn't do that for 5% of their fan base. The devs simply know that a lot of people do solo MMOs and those people often don't do dungeons at all...and they never raid.
A while back a poll was done, the results of which said that between 12-15% of people who played WoW actually raided. I have no doubt since then that number has gone up, but I doubt very much it hit the 50% mark. A lot depends on your group of friend, but consider this.
If someone doesn't group, doesn't join guilds, doesn't post on forums and doesn't raid, who would know they were there. That's the problem that exists for players like me.
There's another demographic of players too, called social players, who use MMOs as basically giant chat rooms with occasional stuff to do. Many of those people don't raid either.
See it comes down to that old hard core casual divide (which isn't really so easily divided since many people, like me, are neither). There are far far more casuals playing MMOs than hard core players. There are far more hard core players posting on forums than casuals. It can lead to a whole lot of misinterpretation about the actual numbers. It has to.
But in the end, casuals are going to pay for games, not hard core players, which is why raids in other games continually get dumbed down and people scream and cry about it. If hard core players really did pay for the game, casuals wouldn't get a second look, but the developers KNOW who is paying their bills.
And many of them don't PvP, don't raid, don't care much about dungeons. You just never hear from them.