I asked this question twice in the other Costco thread and never got a response, so here goes again.
For the record, I would not use Costco's return policy for a "rental" or abuse the policy. I would, however, use it if my TV failed within a few years. A $4k set should not die that quickly, and of course I would not be satisfied with my purchase. I would essentially buy a TV from Costco and pay my yearly membership instead of buying a set and extended warranty from some other store such as Best Buy.
What I'm wondering about is this: can Costco change their return policy after you have already made the purchase and have the new policy affect your existing purchase? For example, you buy a set and 8 months later they change the return policy to mirror their policy on computers. (6 month return policy, if I recall) Since you purchased your set 8 months earlier, you can no longer return your set and are left without the old Costco guarantee acting as your extended warranty.