As far as I'm aware, none of these systems have anything even remotely approaching formal methods used in any of their development; they're merely well-checked systems. Formal methods don't really work for real software, and that's pretty much the end of it.

If you see how much effort it takes to develop even the most trivial of functions by formal methods, you'd understand. As you're just an IT manager blinded by words, you won't.

Slarty