Haven't seen the movie yet but just came across this thread now. I checked out that u/w picture of Jessica Alba in the silvery suit/hood and a bikini bottom, wearing was it Halcyon dive gear?, and the thing that caught my eye (okay okay, besides Jessica) was... her SPG hose was unclipped and dangling.
It's a pet peeve of mine, especially because I see it all the time -- even on NGC, where some of those guys have been diving since forever, they just let their gauges and octopus dangle freely, whacking coral or gathering sand. I see it in movies every now and then, too; last time I saw it was I think CSI: Miami, the guy who does their diving stuff also had his octopus dangling.
Though I haven't seen this movie or The Cave, I agree with those who say you should just enjoy films like these for their entertainment value and not judge too harshly on their technical correctness, because we know they're going to go Hollywood on a scene or two.
(I mean, even in other sports movies, it's the same deal. Anybody see the trailers for GOAL! -- the kid in the lead role does some overly flashy kicks, just for eye candy. But for my money, the best footballers I've seen are not the flashy ones, but the graceful ones, who play with finesse and subtlety.)
Having said that, a serious dive movie would be great too -- technically accurate, with a good script and great underwater photography.
If you want to trash TV/movies for taking liberties with diving, try Baywatch. Ohmygod. They oversimplify things like the bends (including practically endorsing in-water recompression), as usual people run out of air left and right, and the lamest I ever saw, they were TALKING to each other underwater, using normal regulators. Geeeez.
