The disappearance of regionalism?

This weekend I finished How We Talk: American Regional English Today, which was completely fascinating. All this time I'd been thinking "spendy" was a neologism created by Joss Whedon, when it is actually a widely-distributed expression in the northwest! And the mysterious Great Northern Vowel Shift is also explained in satisfyingly clear detail. The book slightly disappointed, though, in not having much to say about great swathes of the country, especially places where I've lived extensively, like Northern California, because the accent and vocabulary in those places has become the national standard. I think this is partly wrong--teenagers, in particular, talk in very specific ways in the Bay Area. (Berkeley High School students, even wrote a Slang Dictionary about it). But he's also right, in that a homogenized verbal landscape vocabulary and pronounciation has come to match our cookie-cutter franchise geography. This is a glib critique, I know, but I think it's also a right one. And if I'm correct that linguistic innovation seems to be increasingly commodity-driven--that is, most new phrases and turns of speech come about in relation to consumer products--it seems to make sense that this would be a move enacted uniformly across the nation as a whole. It's easier to market and distribute a product if you can do it the same way in every town, north or south.