My Mates parent is a childminder, and thats exactly what she does, lol!!
A lot of shops physically dont have enough space to clear the way for them everywhere, anyway. Where i worked, we literally spent 3 hours one night, before sale started, trying to make it so there was enough space for wheelchairs to get through, but we could still get all our stuff that HQ was making us sell, out on the shop floor. It was sooo hard to figure that puzzle out, that making it so double prams could fit through too was near-on impossible.
I prefer the double prams where one baby goes in front of the other, instead of side-by-side... i saw one somewhere and thought it was more practical for shopping, though i dont know how common they are or expensive or whatever...