I do not think this is a recent change. 10 years ago brand name determined what size I was buying - Guess? was always a 32, Gap was a 14...heck, I even have a dress that fits now that is a size 6!!! Go figure???
I have to agree though the sizes have changed - I just went into the Gap and treated myself to 2 brand new pair of jeans - 1 were regular 12's and are pretty darn tight (my current goal is to fit into them nicely w/o baggage hanging over the top), the other are size 12 Stretch Boot Cut and I could have went with the size 10!!!
Style, cut and maker all effect what size goes over my wide-load behind
I LOVE the fact I can claim I wear a size 12 though...