I am not 100% familiar with the Acura / Honda SH-AWD, but from what I understand it is an always on solution and is designed to be used primarily on-road.
The 5th gen 4Runner (excluding the limited) 4WD system is designed primarily for off-road use. The comments [MENTION=122813]nb rob[/MENTION] made are really more to do with the irritations of that system when used on-road / pavement / high traction surfaces as it does now allow slip like a regular AWD car. When in 4WD making tight turns, like in a parking lot, you will notice some binding in the drive-line and resistance when turning. You can experience some scrubbing of the tires, chatter, or jerky motion from the truck. It does that because the front and rear axles are locked 1:1 in rotation.
The Limited allows you to unlock the center differential, making it ideal for use on-road in any type of driving condition as the front and rear axles are not locked in a 1:1 ratio. It won’t scrub, bind, or chatter on road. Without getting into the details, it functions just like any other AWD car on the road… Audi, Subaru, Acura. You still have the option to lock the center diff, which then functions no different than the other 4Runner trim levels off-road.
The solution in the 4Runner for the most part is fully mechanical. There isn’t any “transferring” of power using clutches. It is done using a network of gears called a Torsen differential. This is what is also on the 4th Gen, GX, and Land Cruiser.