This isn't a Costco-specific thing.

HP printers come in an "e" model, which requires an Instant Ink subscription (but is cheaper - effectively subsidized by the subscription), and a non-"e" model that is unlocked (but costs more). Just don't buy the "e" models if you're shopping elsewhere.

In general, the reason Costco sells electronics with different model numbers is so that you can't price match them to/from other retailers. Sometimes a few minor features get removed as well to lower the overall cost.