Exactly - I shot the 5D at ISO 3200, but underexposed by 1 stop. I then "pushed" it in post processing by raising the exposure by 1 stop to simulate ISO 6400. This is pretty taxing on the image, but it can work if you expose pretty high and don't have a lot of shadow detail that you want to preserve. And, of course, your final image size isn't a 2-page magazine spread!
ah ok, i was just about to say ... "what's wrong w/ my 5D?" Thanks for the explain, sorry that I can't read so good today.