what is the difference between a diff and traction control?
 

I noticed int he 4runner ads, but what is the difference? isn't traction control suppose to provide torque to the wheel that needs it when the other is slipping? A lock diff does the same right?

A diff lock forces both tires on an axle to spin with equal power, therefore if one came off the ground the other would keep pulling. You wouldn't really even know the one tire was up as far as traction goes. Traction control systems use the brakes to stop an individual tire and force the power to the opposite side. Therefore if one tire was off the ground it would take a brief second fot the traction control to kick the power to the other side, ie it would be more noticeable. You can kind of do this with an open diff., if you are stuck give it some gas and tap the brakes it may eventually push the power to the other tire.

Yeah - essentially a locked diff is a "mechanical" type of function. It's either on, or off. If it is selectable you have the ability to turn it on or off, if it's a lunch box locker, you can turn it on by simply having your foot on the gas pedal. There is no fighting it so to speak, and you as a driver will have to have abilities to hone it's advantages and disadvantages to push you on the 4wd trail.

Traction Control is a computer sort of technology and it is a reaction from rpm speeds that your computer receives from your wheels and then a mechanical solution by the computer I guess you could say, however you can't turn it on or off, only when the computer senses things are ok will it go off which is probably milliseconds when that wheel without traction regains traction. Traction control in my opinion is probably more convenient and a better on road worthy option. But I think many will opt for a locked diff because it offers no BS, no real serious cost, it can be fixed en route if needed with some tools, and it just plows you right up the hill or through whatever without any crap.