Raymond wrote an interesting post about the erosion of the car trip experience.
Along with the desired to shield our kids from any discomfort, I think there's a big desire to shield them from boredom.
Boredom is part of being an adult, and I think learning to deal with it is an important part of growing up.
Back when I was a kid, every year or so we took a long trip from Seattle to Boise to visit my grandparents. Though we usually made the trip over in the night (to avoid the heat (no AC, of course)), there were lots of hours of watching the "scenery" roll by (as an adult, I find the area around along the Columbia river to be striking, but as it kid it's a whole lot a nothin'), and then similar hours while we were there.
That meant we have to learn how to amuse ourselves and not annoy each other too much.
But if you have video every time your in the car, you don't learn how to deal with being bored, and (as a parent) you miss some great opportunities for conversation, not to mention the chance to inflict your musical tastes on your offspring.