Final update for now. After getting no response from Warner Bros third-party support (the people dealing with the boxset issue but not the standalone problem reported here) I called Fry's back and asked if they could check a copy of Goblet there in their PS3 before I came back for my second return. They said sure, they'd call me back - and didn't.
So yesterday, I called and talked to the returns manager. He said they had a copy that they tested in the PS3 and worked but suggested that my issue could be due to differences in PS3 hardware. I have the 60GB unit with backward compatibility (essentially a launch unit, except I bought it late - a couple months before they discontinued it). He offered a refund if I wanted it. So today I drove down and asked them to try my defective copy in their display PS3 (a newer hardware config without backward compat and a different hard drive size). Sure enough, my defective copy loaded and played just fine!
So I took the refund to prevent any more 40-mile round trip returns. What's vexing is that I really want this movie. I saw it in the theater at a really late show and enjoyed it, but was quite sleepy. I've been wanting to see it again in hi-def for a year now. I will probably wait 1-2 months, keep an eye on this forum in case there's more news of a fixed version (a method to tell would be helpful!) and buy it again someplace closer to my house so I can more conveniently return it 10-20 times, if needed.
Now I am testing every BR disc I get right away to ensure all discs load and play! So far, Goblet is the only one out of nearly 100 discs tried that has failed. (I did get a faulty copy of Black Snake Moan from Netflix that skipped, but I reported it damaged and sure enough the replacement copy worked fine.)