Anyone saying that Postel's law is one of the reasons that the web is robust needs their head examining. It was a terrible idea that has been plaguing browsers for a long time.
You are absolutely, categorically wrong; I am certain of this. Your comment is about as wrong a comment as I have ever seen on this site with a positive comment score. Building the web without Postel's law would be like trying to build a world wide web solely out of CORBA and/or DCOM. The costs of specifying, synchronizing and communicating machine formats would have dwarfed all productive work.
But it's academic in any case; any web that anyone tried to engineer without something along the lines of Postel's law would have been outcompeted very early by one that followed it. A strict web would have kept too many marginally qualified people out and would have had much smaller returns owing to lack of scale (Metcalfe's law etc.). Keeping marginally qualified people out means they are strongly discouraged from learning (instead they give up), and that would throttle any possible growth.
