Re Champagne bottles at Titanic depths: They're built strong on purpose to contain the pressure from the contents. Given that it's more difficult to make something which can withstand pressure from inside than from outside, it doesn't surprise me that the bottles have survived intact.

What I'd like to know is whether any seawater has made it past the cork into the wine, which (come to think) would reduce the pressure differential; this would help preserve the bottle, if not the contents. And No, I do not volunteer as a taste-tester.