In electrical, plumbing, etc, supplies like that, you are absolutely correct.
But in appliances, for example, the model #, SKU, and barcode number are the exact same. Two "like" items can not have the same barcode.
Case in point: Barbie Dolls. They look identical. Same packaging. Toys R Us has one barcode and walmart has a different barcode.
The difference? The cheaper item from either (usually Walmart) may come with less accesories, for example. In the Barbie case, the pink teacup set is probably left out. Or something like that to that effect.