Here's what I was told by someone in a position to know:
\"Stoned couldn’t get a proper location release for Costco, so it’s not so much the issue of clearing the brand name, but rather identifying the location.\" That, according to this source, is the reason why Costco had been mentioned by name in earlier shows, as well as why they didn't have a problem identifying other brand names.
BTW, out here in the great midwest, we don't have Costcos. Our bulk discounters are Sam's Clubs, an offshoot of Wal-Mart.