You can actually leave your grocery cart in special spots in the middle of the parking lot in each supermarket in Bulgaria as well. It's just the fact that you don't actually drive in Sofia which makes you think it's not possible :)
As to parking spots we should consider the fact that 2 million people live in Sofia and its a capital and almost all institutions, buisnesses, students, diplomats are here. If you go to a provincial town you won't have any troubles finding a place to park, I'm sure :)
I also wonder if there is a difference in the quality of food apart from prices?