I'm not convinced about the seats not being able to raise because of the air bag system - why?
I'm sure that you can raise/tilt the steering wheel.
Therefore, the geometry between the seat and the air bag can still be changed - the seat still slides, and that affects the geometry - so the airbag will still hit different people at different positions (people have always come in differnet shapes & sizes too).
In my opinion (I'm in the automotive industry), it's a cost reduction. And you NEVER tell a customer that you didn't want to do something because it cost too much.