They don't technically have a lifetime warranty, but this is what I have gathered:

Costco will accept returns within 30 days. However, clients have told me that they have brought things (electronics in particular) back up to a year later and gotten refunds. Beyond a year (as in lifetime) I can't imagine....

After being a warranty servicer for many brands for a long time I would consider the trouble that generates for the manufacturer and the servicer.

The manufacturer, because of the size and buying power of Costco is stuck with old merchandise that needs to be refurbished and sold again as B stock. The servicer, who hates warranty work at 40% of his regular repair rate and waits expectantly for a repair to come in out of warranty, gets this "store stock" warranty repair which, in the case of video, might be out of the 90 day labor warranty, but instead is "store stock".

It makes Costco a great deal for consumers, don't it?