Her rant and Mod Squad post seems anti-derivative, but derivative games are what make the market go. They key is in HOW they are derivative. Here's a list of games that are derivative + something else.
* UO = MUD + graphics * Everquest = MUD + 3D * DAOC = Everquest + compelling PVP * WOW = everything + high production values
The key is in the "+ something else." In all those cases, I'd argue people either didn't know they wanted the additional features, or didn't believe they were possible. So, being derivative is fine, as long as it's on a vector nobody expects.