It's not even such a "similar concept". SL's "resources" are just... money. Real money. And it doesn't really have any inherent "gameplay". It's a pure sandbox -- with dollars for grains of sand.

Notch is talking about real resource management issues, combat as an inherent part of the game, random AI encounters, etc..

This is a game that happens to share some SL-like properties. SL is just a framework. Arguably that makes SL more interesting in some ways, but it's also a lot harder to "get" something out of SL other than pure socialization.