As noted it varies from place to place mostly depending on how smart the people are. As you said you don't want to start a debate about the alleged benefits of "High test" but many folks just insist that their modern, tuned for regular, cars run better on the more expensive stuff.
Others actually measure miles and gallons and know the truth. (I'd guess you are among them). So the stations have to mark down the high-test in an attempt to lure some of 'em into over paying,
That said. Yes there are still some "Tuned for high test" cars out there, and some still being made that need high test.... Out of my price range however.