I don't get it either. If it's an option it is, and there will be buyers if it's intriguing and done well. I'm a singleplayer type of girl normally, but I have played some online role player games so if I pay for a game that does both. I'll try it both ways. I might like it both ways.
The "matchmaking" sounds intriguing to me. It would be really cool if they could group players per preference in a front ended manner. Perhaps you end up in a world more geared to you and others preferences (that match). Not sure that would be suitable for the sims and no where in this article or blog post does it mention the sims will be done this way.
Although again .. I wouldn't be surprised if it were optional.
I'm seeing shades of secondlife though .. and unless they police or control a world anything akin to that more heavily for performance for various users, flow, and actual gameplay being managed and actively encouraged. I don't see it being all that more than a second .. secondlife.
If they apply this smart AI though .. to single player and even multiplayer games with the world changing in a way that makes sense (some might not want it to make sense). It could be interesting.