I don't think it is a new phenomenon, but I do think the explosion of interest in breadmaking and sourdough has muddied the waters a lot in the past year.
Yeast-risen breads fall into three categories:
wild yeast starters, ie, sourdough (This also includes 'old dough' recipes.) Historically, all yeasted breads were once sourdoughs.
commercial yeast This is a relatively new trend in baking, because bread has been around for thousands of years but commercial yeasts for much less than that, they were developed as an ofshoot of the brewing industry in the 18th or 19th century. Brewing yeasts and baking yeasts have evolved into products designed for specific usage. If you visit a homebrew shop you'll find many types of yeast, I'm told none of them will work well in baking.
hybrid doughs that use both wild yeast starter and commercial yeasts. This is done both for time considerations and to de-emphasize the sourness, though there are other ways to do that as well, such as Chad Robertson's 'young or immature starter' method.
I exclude those that use chemical souring methods to try to mimic the acidity of a bread with with sourdough starter in it as unworthy of inclusion.
Historically, many rye breads were pure sourdough but that's not necessary, the rye bread I make the most, Reinhart's marbled rye from BBA, is a commercial yeast bread.
Of the 78 bread in Ginbserg's The Rye Baker, a dozen or so use only commercial yeast.
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