It's definitely a Michigan thing too. I'd bet people in Wisconsin and northern Ohio do it as well.

And not just northern Ohio--Daytonians and Cincinnatians routinely shop at Kroger's* and Meijer's.

*And then you get the handful of arch wiseacres--the same sort who patronize Tarjay and Skullini's Chili--who refer to the gentrified Kroger superstores as Krojair's.