> I notice that by far the most common change made is enhancing colour saturation. Every single picture is made more vibrant by retouching. After that, I notice the shadows are greatly reduced if not entirely eliminated, which also contributes to the general sense of "brightness" and saturation.

Yeah, I noticed this too. I also noticed that most of the original photos are pretty badly shot. Either composition or exposure wasn't done very well but it was all fixed in the final product. (Like the one with the three girls at the sink. The faucet was in the way and there was a distracting room off to the left, that was removed in the brushed shot.)

I guess it's cheaper to get your airbursh guy to fix all that after the fact rather than to hire a good photographer.