DrBarr, two things your overlooking is that
1) air in the liquid causes the liquid to become pressuriazed. that does not mean that there is any savings in space the liquid takes, but that the space inside the liquid is taken up by the air molicules. depressurizing it allows that air to come out. if you want to see this, take a soda bottle, shake it up and open it over a container large enough to take up the liquid as it comes out. after it settles compair it to an unopened bottle of the same type of soda. If you have a sensiative enough scale, it would show that the opened liquid is lighter than the unopened one, but they take up the same amount of space. the co2 in side the unopened one makes the differences
2) denser air means more molicules, which means more weight. when the door opens the air will equilaze but not immeadiately. doing so will cause the water in the ice tray to have a little more push to freeze. not much, but some. have you even open a freezer in a humid, hot enviorment, and watched the vapors fall towards the floor, usually disappating before the get far? that denser air heading for the lowest lvls.
as far as the water bottles not being pressurized, it depends on where the water was bottled. If it were bottle at sea level and your at high moutains, there is considerable amount of pressure difference. if they are in the same town and the day the water was bottled there was a high pressure ridge and you opening it with a low pressure weather pattern around you, there would be some differences. perhaps even enough by itself to cause freezing.
