iTunes video file sizes?

I tried a quick MRoogle on this one, no luck for what I was looking for. I'm trying to figure out why iTunes video sizes are so ginormous...

I recently got addicted to the show Chuck, so I bought the 2nd season on iTunes...

Now, I've downloaded tv shows from other... ummm.. sources before, and it typically is about 375MB for an hour long show (45 mins really..)

But iTunes, I'm running into standard def video in the 600mb for the same length of time.

Is this due to iTunes encoding or something? I mean, granted the store seems to pipe out the downloads pretty quickly, but its still a pain to wait for a longer download than if I'd obtained these through questionable methods...

Just looking for info, thanks!

 

Thanks dude