Where to Find a Pet Health Store

Why is it that you don't see a pet health store on the corner like regular drug stores? There are probably more than half the population of pets as there are people in any neighborhood. I guess the market just isn't as big. Do pet owners not like spending the same amount on their pets as they do on themselves? The best opportunity I've seen for health product marketing is through national pet stores, like PetCo. Veterinarians carry necessary pet products at times but they aren't always open and available. Then again I guess a pet doesn't have the means to get up and buy Tylenol when they have a headache.