This is not exactly true, the Limited in H4F does not have an *open* center diff, it has a *limited slip* electronically-controlled center diff. Minor but significant difference.
As you said, Limited's "H4L" is identical to the SR5's "H4", and "L4L" is identical to "L4".
It's not electronic, except that you can electronically lock it with a button. It's a Torsen limited slip differential, so it's similar to Audi Quattro systems. The limited slip functionality is all mechanical, and it's instant. Basically when you apply torque to the input side it sort of locks up (it can slip a little, so it's not rigidly locked). If you are coasting it works like an open diff.
I am thoroughly impressed with the Multi-Mode 4WD in the 4Runner but am curious as to the limitations of, or best use of, the AWD mode. Is it to be used only as an extension of 2WD in a driving rain, dirt roads, etc. or does it have more capability before dropping in 4H mode?
My concern is stressing AWD components beyond their intended use. Anybody got some technical info on this subject?
It doesn't have any friction material to wear out, supposedly never needs service except for changing the transfer case oil occasionally, and it's very strong. I haven't heard of even a single problem with them on the 4th gen. I asked about how strong it is here:
http://www.toyota-4runner.org/4th-gen-t4rs/181476-limited-slip-center-differential.html
It's way better than 2WD, and it's way better than the weak AWD systems on a lot of crossover SUVs.
The center diff helps you maintain control in the snow. See here:
http://www.toyota-4runner.org/4th-gen-t4rs/213095-need-help-h4-understanding-driving-snow.html
There are probably collectively 50 billion miles on US 4th gen 4runners (multiply the sum of 2003-2009 sales figures by an average of 100,000 miles on each) and I can't think of anyone on here complaining about the center diff. The actuators are known to be an issue, but that would be the same for any electronically actuated transfer case.