Why is You Tube video sharper than iTunes purchase?

Here's two screenshots of the same video. The one on the left is from You Tube and the one on the right is the one I paid for on iTunes. Why is You Tube video sharper than iTunes purchase?

via iLounge Forums http://forums.ilounge.com/itunes-related-mac-pc-applications/278543-why-you-tube-video-sharper-than-itunes-purchase.html