Pretty much what's already been said here, but I also think that private servers are still worth it.
Sure, iRO is free now (with very severe restrictions on what you can and can't do, so you still pretty much have to pay to win the game), but those with true passion and innovation can make a server that will completely recreate the feeling of RO. That's what we're trying to do with ours. So many things can be done with scripting and modifications that the possibilities are almost unlimited, you just have to have the right team to bring it out.
New story lines, content, explorable worlds and so much more. All of these things can be brought out with the right minds working together, and I think, along with nostalgia, is what keeps players around. The next best thing. What will the next server come up with? How will my experience differ? If they weren't even slightly interested in that server advertising, "UNIQUE PVP AREAS," then no one would still be playing. I guess it's just all about the curiosity. It was always a mixture for me, curiosity and nostalgia.
Not to mention, I don't know about anyone else, but I get a very high sense of satisfaction from what I do. I work with customer service in real life, and I just love working with players as well. I love working my tush off to bring them the next best thing, discussing mechanics and inventing new ways to do things. I also just love the old-fashioned feel of being on a staff and connecting with people, helping people. Though, that's just me, I've always been told that my philosophy on administrating was a tad cheesy.
BUT ANYWAYS. That's just my two cents.