Tire Pressure Light On problems of the 2008 Toyota Sienna

I bought my 2008 Toyota Sienna in October 2007. The first defect I noticed is when the rear windows are open, the rear doors do not lock in place when you open them. The mechanic stated said the he thought the reason it was designed this way was as a precaution, in case a child is leaning out of the window when the doors are opened. This made no sense. My experience has been that the door slams really hard and then bounces back. If a child happened to be leaning out the window they would suffer serious injury because of this. No one has been injured thus far, but the slamming certainly startles everyone! this happens even if the window is only open slightly. Another defect is the tire pressure light on the dash. It stays lit up constantly. After adding air on numerous occasions, I noticed that the light comes back on in just a couple of days. I discussed this with the dealer and he simply stated that tire pressure changes with the temperature. This is a safety issue because I would not know if the tires' inflation was really off or not. Obviously I cannot add air to the tires every other day.