I've had the Costco "prime" meat in several cuts....doesn't taste the same to me....can't really put my finger on it...BUT it just doesn't seem to taste the same as other prime meats....maybe it's just me.
Could have been a weird batch, too. I buy a lot of steaks at Costco (go carnivores!) and buy USDA Prime graded steaks whenever I can -- some ribeye, some strip, some sirloin (if the wife insists).
There are times I've gotten Prime and it wasn't that good (flavor or texture) and times I've had to buy Choice and it was fantastic.
Costco is also the nations largest wine retailer.