Ya know, as a father of a 7yo boy and a 9yo girl who together have put in about 40 hours of lego building in the last week alone, using lego from my childhood as well as a dozen kits purchased in the last 5 years or so, this simply isn't true.
Its not true that the pieces will only ever fit in one way.
The reality, I've come to realize after playing with these things quite a lot recently, is that they're simply 'higher-resolution'.
For instance, I have watched this brick (from a Star Wars ship)
http://cosmicbricks.ecrater.com/p/11804345/lego-dark-bluish-...
become variously, a foot, an ear, a beak, part of a dragon's wing, part of a temple, part of half a dozen spaceships of completely bespoke design, part of some sort of epic death dealing mechanized tank/robot thing, and probably several more models where I didn't even notice it.
Whereas I had to be content with "8-bit" round shapes with my old Lego brick pieces, my children and I are able to produce models with much higher resolution - and that're pretty satisfying.
My kids play with these "model" kits by building them as per the instructions, learning a few new construction techniques in the process, playing with the finished model for a day or two, then tearing them apart and applying any new techniques they discovered into their constantly evolving storyline.
Just like Dad did... does...