There's absolutely a difference. Going to Costco is a monumental hassle compared to Dollar General. They have few locations so for most people it's a farther drive. There's a line of cars snaking around the place waiting to buy gas. The parking lot is huge and I have to walk through it. Once inside, I have to pass the giant-screen TVs and half a warehouse of rarely-purchased items before I get to the food. All the food is in huge units. Often the lines at checkout are extremely long, and then there's another line to have my receipt checked before I get out. Then I have to load the stuff into my car - they don't bag it. Oh - and I paid a membership fee to experience all this!

Dollar General has many multiples more locations, and I can park right in front of the door. I'm in Costco every week and it's fine but yes, that walking time combined with everything else is definitely a factor.