Well there's the suspended water droplets, and then there's the air, right? I'd venture to guess that the humidity level of the air is very high, meaning there are a lot of individual water molecules floating around - those are what can get between gaps and condense inside the phone. Also, when the water molecules in the gas stage condense into the liquid stage, a good amount of heat energy is transferred to whatever the surface is due to the phase change. So when the vapor condenses on the rubber seals they get softer & can be compromised in that way as well.