We'll find some item that we like there only for it to be completely gone 3 months later and never to return. While at another local Costco they have palettes full of it. 3 months after that the product will disappear from all Costcos and a different, but better one will show up everywhere. Things like Wine selection will also differ quite a bit from store to store.
That or there will be sudden changes to the packaging of staple items in the store for no real reason. Milk, for example, seems to get a packaging overhaul every year or so.
Either way, even with limited choice, over time the number of products you might buy at a Costco turns out to be quite a few.
Other retailers, on the other hand, are surprisingly more uniform in their product selection. The half dozen Targets in my area offer more or less the same products and fit it all within 1 or 2 master floor layouts.