I have not seen it with electrical, but there are some ittems that are different than at the supply house. Lowes sells an American Olean tile in the "Sandy Ridge" series. It does or did sell for $1.27. The best I could get from the supply house was $1.79. I know the guys at the supply house and they said the color variations were of a wider range for the Lowes tiles. They also had a bit more size variation. 1/64" variance instead of say 1/128" variance. It is not some much that the quality is less...the distributors simply got the tile that was more color matched and the better of the fired batch.
I also hear that tub shower valves are not as well made, but I can't see a difference other than retail packaging as opposed to wholesale packaging.
One other item is the manufacturer give new numbers on a per retailer basis. So then they don't have to price match because it is not an "identical" item. Different UPC...different item.
c2500