You gotta love this movie. It pretty much fulfills Phil's often cited nit killer, "it was all a dream", so many nits you could account to simply the fact that they are in a dream with any gaffes explained by that. Not all, though.

One pleasant surprise was the performance by Tom Hardy, i.e. Shinzon from Star Trek: Nemesis. Very entertaining performance. He's been nominated for Spike's Scream Award for Breakout Performance.

Why do they need to breathe air when they are underwater? They shouldn't, since they know they are dreaming..

It's currently playing on HBO, and has been for a month or so. It's also available On-Demand. Which is how I watched it this afternoon. Superb special effects. But - was the whole movie a dream? The suits, ties and dress shirts that the men wore were first class, but the credits (IIRC) did not name the clothing supplier (it sure wasn't J.C. Penney, where I bought my last two suits. ) Also, the pic seems to tread ground kinda similar to a 1984 movie titled Dreamscape, which starred Dennis Quaid and Christopher Plummer.
Here's a review from Eccentric Cinema. It's that review that got me to watch this film.
This film is rated PG-13, assumedly for adult situations and violence. But, there is nothing in it that would have merited higher than a PG rating not too many years ago. (BTW, Dreamscape was the second film to receive the PG-13 rating. Which I felt it deserved.)

If they will wake up when they feel the "kick" ie the feeling that they wake down, couldn't they wake Saito by throwing him ?
Instead Cobb only mentions shooting him, but that would land them into "limbo"...
Why did they forget the "kick"?