while I doubt it's the same for cats and dogs, my girlfriend and I have noticed that many of the downtown pet stores don't offer healthy food for our two guinea pigs. We have to go to Yonge and Eglinton from the harbourfront once a month and stock up on the proper pellets and hay. We've asked other pet stores if they would be willing to put the brands we need in their stores (essentially, trying to educate them on the proper food for small pets) and all of them either said no or that they already had enough of a supply (even if its junk).
To us, it's one of two things: they don't feel that small animals need to be fed a proper diet because they're so easily replaceable, or they just aren't educated on what animals really should be eating. If either one applies, I don't see how someone could operate a pet store. I could understand if they offered both healthy and unhealthy options (since our very own grocery stores do so), but to completely ignore the healthy ones disturbs us quite a bit.
Mind you, cats and dogs are far more popular, so odds are most stores will stock a good variety.