This problem can happen in both 2WD and 4WD vehicles, whenever a driven wheel is placed on a surface with little traction or raised off the ground. The simplistic design works acceptably well for 2WD vehicles. It is much less acceptable for 4WD vehicles because 4WD vehicles have twice as many wheels to lose traction, increasing the likelihood that it will happen. 4WD vehicles may also be more likely to be driven on surfaces with reduced traction.
It sounds like they are saying if one wheel out of the four in a 4wd loses traction, it will be the only one to spin. Not true.....the rear is locked into the front, but it's wheels are independant of what happens in the front. As long as the rear wheels have traction in 4wd, they will provide movement, not just sit there while the front spins. Vice versa....only if a wheel in both sets of axles with open diffs loses traction will it sit there and spin.
2001 Ranger with some stuff (RIP, some pieces still floating around)
2004 Level II and an 05 Rubicon with some stuff.