RuneScape recently added its 26th skill, Divination, which is old news now but sticks in my mind because for some odd reason I didn't think of RuneScape as being a skill-based MMO. That's probably because I only played it for about 15 minutes circa 2002, though.
In any case, skill-based MMOs are rarer in 2013 than they were in 2002. Pitting them against their class-based counterparts might make for an interesting Leaderboard, though. And if not, hey, you can still berate me for the lack of poll choices! Vote after the cut!