I'm not sure how legal this is, but I don't know the policy on mentioning other network's shows on here. But here I go.
A few years ago the BBC program Top Gear did a sgment on a car going into the water and if you could get out. In general they came up with the same obvious results, you have to wait for the pressure to equalize.
BUT, the power windows did not function on the Vauxhall Carlton. COuld the circuits be different on the Taurus the Myyhbusters used? Is there a fundamental difference in the Vauxhaull, or in British/European spec cars in general that cause the electrical system in the windows to cease functioning?
Similar statistics exist in the UK regarding cars going into the drink. More people int he UK drown in their car than in boats.

in the following video the electrical system appears to go crazy - locking the doors!

http://www.youtube.com/watch?v=oyx1E2s-tsE

My grandfather refuses to buy power-window cars. Part of its expense, but another reason is this myth. He always told us to just roll down the windows if you go over a bridge. Did the Mythbusters try manual windows?

Yes, Adam and Jamie tried power windows and manual - the manual windows didn't work underwater because of the pressure and the gear broke. Power windows didn't short out, that simply didn't have the strength.
But maybe your grandfather is partially correct. If the power windows along with the electrical system fail - you're screwed. BUT, the inside of the door won't fill up instantly, so there would be time for one to hit the switch right after impact with the surface. IMO that would be beter than having to roll the window down manually. Hitting the switch would be faster and take less effort.
The Vauxhaull the BBC team used was from the early 1980's (or was it 78?) so maybe modern cars are different.

Another possibility, Euro spec cars have a mercury switch that detects when the car is flipping and unlocks the door, because Richard was able to climb out - unless he unlocked the doors manually and I didn't notice.


However... In my opinion I believe the Mythbusters test was flawed and inconclusive with respect to the electrical systems.

Then again, where does one find a newer car that is willing to be dunked. Maybe just a dor test?
But we don't know where the fauilure occured in the BBC test... water could have hit the ECU.

Who cares if BBC tested it first? The Mythbusters test was probably more interesting and more scientifical and proffesional.