Sure, it *CAN* pay to drive around, depending on the situation, how much price difference there is, and on what your knowledge is of what things cost at each of the locations.
But acquiring that knowledge takes time. Driving to those places takes time. Driving to those places takes gasoline.
Now if you know from past experience that location A will always have significantly lower prices on certain items, and location B will always have significantly lower prices on other items, and location C will always be competitive on certain other items but will also have higher quality, and the distances between them are short enough to make running from one to another to another practical, then fine.
But if you live in an area where the stores are relatively price and quality competitive, like where I live, you're not going to see that big of a swing in prices from one to another--and when you do, it's going to be short-term, you'll have to spend considerable time researching the prices to find out who is low on which items at that point, and those differences are typically pretty small. In which case, you're having to spend more time researching to find a smaller price savings. To where the savings per hour of your time are well below minimum wage. At that point, it's not laziness to say that your time isn't worth it--rather, it's simply a realization that life is too short to be spending so much of it on such endeavors.
TJR, of the stores you listed, I'm only familiar with Costco, but for there to be a $50 - $100 estimated savings on your trip, it sounds like you have enough pricing variety in your area for it to be worth that. If I had purchased those same items here, and driven around to the stores available to pick out only the best prices, I probably would have saved $5, with almost no difference in quality, and a shopping trip which took twice as long, when I could have instead have gotten something done at home or spent more time with my kids. That's not worth it. And Hugh, that's not laziness--it's simple common sense.
So yes, I agree, in certain cases it *CAN* pay to shop around--but in certain other cases, there's absolutely no way to justify it.