Also, why just vehicles? Mechs suffer from the same difficulty.
Not really, mechs stay level as they walk. They don't have to adjust vertically for the terrain as tanks do.
I wouldn't be opposed to some automatic pitch correction for tank turrets, but complete stabilisation wouldn't be interesting, as -SM-SUCKER points out.
I think the tanks' handling is a much worse problem, I seldom use them because the way they (do not) turn, their weak torque, how they slide down form hills and the occasional ridiculous bouncing. I wouldn't mind more nervous and manoeuvrable tanks, it would more than offset any difficulties with the turret handling.