I have to disagree. I don't play online games myself, but the people I know who are active players certainly seem to consider the interaction between players the main part. They even choose the game to play based on what their clan/guild/whatever is playing.
UO is the game people play to interact with those who are not in their clan/guild/whatever. UO is the game where people role-play as blacksmiths and merchants, selling their wares and services to total strangers, decorating their homes and outfitting them with "rune libraries" to make them more appealing to customers and generate foot traffic.
When I walk around a player-built town in UO it feels lived in, something I have never been able to say about any other MMO I've ever played. In this regard, UO is more like Minecraft than (World of) Warcraft.
What I mean is that UO (at RP servers) is more like mass theatre. You actually play the character, you meet others, you go fishing, steal eggs from neighbours farm. Went on walk and get stopped by PK, killed and robbed together. It is very different experience, very unique to UO.
