Those extra world files were placed because you installed the worlds more then once. The Riverview.world was already in the world folder, when you used the launcher to "reinstall" them it created the Riverview1.world file so as to not overwrite a file already in that folder. Before you install a world for a second time(or third) you should go into the folders Moryrie listed and delete the old world files. That goes for any worlds, not just EA ones.
I can see that happening. I had thought though, that if you tried to install a .sims3pack which was already there that you would get the "...".sims3pack is already installed error in the launcher, and that file would be ignored. I guess this isn't always the case.
My Store content folder contains about 450 .sims3packs (If only compilations were made sooner) I had a corrupt file somewhere, so when I replaced it, I just reinstalled everything, thinking that the corrupt file may have caused things to stop at a halfway point without installing the rest. I figured it'd be safer to just reinstall it all, and let it ignore or replace files already installed, since I had so many sims3packs. So that's probably how it happened.
I'll definitely keep all this in mind next time around, at least I now know what was going on and how to fix or prevent it.
By the way just noticed I put this in the wrong section. My apologies.