Heh! Well I suppose that fits with Wiggo's comments. "I was losing fitness just cruising back in the pack all week, so we decided to do a bit of work for Cav today." <or similar>
I guess that on flat stages they only have to ride hard during the more technical sections, i.e. where there is some benefit to be at the front, thus (hopefully!) avoiding crashes. And in the last 10km (which are often also technical this year, it seems.)
A week of mountains should please them.