Oooh, wine pedantry! I'm in!
You forgot to mention the Cornas AOC, which permits only 100% Syrah. It's also unnecessary to single out Sancerre, as the entire Loire Valley tends towards single varietals, as well as Alsace. And pretty much all of Germany and Austria.
But yeah, blends have always been the rule, rather than the exception, for even the finest of wines. And one of the dirty "secrets" of the wine world is that EU regs (as well as those for most of the world) permit single varietal labeling with only a minimum of 85%, so excepting a specific region's laws or producer's practices, you could very well getting a blend of some sort, anyways.