The softening of a raucous laughter look is not a scowl. I agree with those who are glad Kate is smiley and laughs a lot in public. I just don't think raucous suits her so well as something, well, less raucous-looking.
A raucous look is, as people suggest, appropriate with a bunch of ruggers but in so many of the photos of Kate the look is of raucousness rather than just enjoyment.
Just my opinion and, as I suggested above, I don't expect people to agree much.