TV Show download sizes. HD vs SD?

In the article for download times it says that a 45-minute SD TV show averages about 200 MB and that an HD versrion averages about 600 MB. When looking at my iTunes collection I've noticed that this is highly inaccurate. Every TV show downloaded from the iTunes store that is about 45-minutes and SD ranges from 450-650 MB (varies due to length of show) and the HD ones average about 1.5 GB. Is this right? Does the support article have the wrong information? I'm finding that shows are taking up more space than Apple says they should and don't want to lose so much storage space on my hard drive.