It's decidedly not a fad. I don't know. Families with drinking-age children will drink with together. I didn't see too many at bars past ten or so, but plenty of families get together and drink at the beach or on the boat and whatnot. They'll do the same at football games and such as well. I don't think that's unique to the south, however.
In Minnesota there are some gorgeous farm-raised Nordic beauties. The University of Minnesota, by sheer size, has a ton of hot young women. Stop by the lakes in Uptown Minneapolis after work or on the weekends and you will be amazed by the number of fit girls out jogging or tanning. Of course we have our fair share of trolls with tits but overall I'd say we have it pretty well, especially in the Twin Cities. This thread makes me feel like I need to visit the South more often though, just to find out if the ladies really are that much better. This is not unique to the South.
Maybe its a water thing? Parent's own the boats so kids party with them? I too notice my friends in Florida have an inordinate amount of Facebook partying pictures with their parents. Maybe the drinking locations co-mingle with young and old more there. Most places I go there are young 20's bars and the ritzier upscale places parents drink at in different parts of town.
I guess it is more noticeable because there is a mother/daughter sweet spot where both women are remarkably attractive, so it stands out more. That may be it. I have a couple of coworkers who are stand-alone attractive and have knockout daughters. I start doing mental math when they're together because I have to justify how she had her and I wouldn't be ashamed to fuck either.
I think a smoking mom with a hot daughter is all about age at which she had the kid. If she had the kid at 24 vs 36 there may be a difference in apparent attractiveness when the kid becomes legal.
We see the mother/daughter thing all the time in my bar. Maybe it's a product of the beach and being on vacation. And truth is that you see it more in the afternoon and early evening...then again the island I live on rolls up the streets at nine o'clock. Just to get away from the Florida bashing for a second, if you haven't read the Amazon review that Shimmered linked in the Tibette thread, you're doing yourself a disservice. It's one of the funniest things I've read in a long while.