Yep. But I don't associate the monthly fee with the social aspect. If I wanted that, I'd simply sit in a chatroom. The monthly fee is justified in my mind by the additional content that is added, the economy that is stabilized by a team of GM's, and servers that are stable.
I enjoy single player RPG's, but when I am done with the main story, there isn't anything left for me. The character I just played is pretty much dead in my mind. An MMO makes me feel as if my character is taking part in a living, breathing world. My character has a lot more room for growth. Since I have never hit a level cap in a MMO, it feels more like an endless adventure. Eventually I may tire of the gameworld, but it may take years, and the world will go on even without me. That's the big reason I enjoy MMO's.