A deer that has a hole in both lungs will die. I don't think anyone can argue that. But the adrenalin rush or flight response can produce different results in each individual situation. This is the exact reason why some people have witnessed a double-lunged deer travel more than 150 yards after the hit (or a heart shot for that matter). Of course this is not the norm, but it has been known to happen. I myself, have had a double-lunged deer travel close to 100 yards. I've also had them drop in less than 30! My point is each scenario is different. Take the best shot that is offered, and don't always wait for a 'better' shot, when a perfectly lethal shot presents itself. I have been bitten more than once thinking I would get the more 'preferred' shot.
I'm not sure about the diaphragm theory, but I know that a liver & one lung will cause a lot of blood loss, a quick kill, and a good blood trail (providing there are two holes). I think my shortest recoveries, statistically speaking, have been from this shot.
A few things that I try to keep in mind when shooting at game is: two holes are better than one, a low hit is always better than a high hit (unless its so low that it misses the vitals or target completely, in which case the animal has a very good chance of surviving; so aim low!), and pick a spot aiming for the exit hole.
There are so many things that can go wrong, and usually do, so we need to try and keep it as simple as possible, and have fun while we're at it. That's part of what makes bowhunting so great.