prompted to install rosetta?

I was just trying to install a program called resize! for mac. It prompted me to install rosetta. I had never been asked to do this before, and it looked like it was doing a regular software update when I did.

Is this just something I have to have for older programs? I installed it and it works, i was just thinking it was baked into snow leopard.


edit - looks like this is the case. you have to install it for older programs.