Costco's discount on iPods was nothing special, and didn't require too much work to find similar discounts elsewhere. The one benefit to buying from them was their return policy.
The Costco folk may have characterized it as a pricing/MAP issue, but most have speculated a dispute over iPad sales (or lack thereof) was the real reason for discontinuing iPod sales.
Costco's not afraid to play hardball, as they showed with Coca-Cola.
They'll probably kiss and make up at some point, but in the meantime, there's no shortage of places to purchase iPods.