Main advantage of auto changeover stats in resi applications is, if the deadband is set right, homeowner doesn't have to worry about manually shifting between heating or cooling. In my own climate at certain times of the year it can be warm and humid during the day, requiring a/c, and a "blue norther" blows through in the evening, dropping temperatures overnight to where the house would be chilly if the heat didn't come on. I've also lived in arid climates where in winter the night temps were in the thirties and the day temps pushed into the eighties, perfect for auto changeover.
Far as I know, auto changeover stats have been available at parts houses for years, meaning any contractor could've bought one and stuck it into a resi app at any time if he so desired. I think with the advent of everything going digital, and the concurrent feature-laden approach taken to sell this stuff, more homeowners are wanting to see this kind of control at home.
I also don't think you'll find auto changeover stats at Home Depot. Thank goodness...hard enough for DIY'ers to change a stat without blowing a fuse or xformer...sure would hate to see a handsome stat like the 8321 go up in smoke.
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.