[thejeff]

Turtling only works in the long run if you can clam (the other gem producers to a lesser extent).
Sure, getting in protracted wars too early is a big problem, but you need to keep expanding your economy. If you can clam, you can do that without actually taking more territory, since gems become the real resource later in the game. If you can't, you need to get more gems by taking territory, which means fighting other nations.

I think 'rush' is generally used to mean very early attacks, to take an opponent out while most are still in the indy expansion phase.
While "turtling" usually is used for a strategy of avoiding war, after the initial expansion, until the endgame.
Most strategies, whether more or less aggressive, lie in between.