That's exactly what I've been seeing in my log files, and the opposite of everything I expected. Most of my pages are oriented towards entertainment, or information that doesn't relate directly to business, so why don't I get a peak at weekends?
The coming Christmas break should shake up these trends as people are stuck indoors due to the weather, but travel more too. If they shop online as much this year as is predicted, we could all see a boost in traffic, but time will tell.
It's not really clear to me what they're measuring, but in my experience Mon-Tue-Wed are the biggest days. I think much of the reason that weekdays are so strong is that more people have high-speed access at work or at school than at home, and therefore simply generate a lot more pageviews.
But Saturday bigger than Sunday? I don't think so.