Postel wrote it in 1980. (First found in RFC760[1])
Since then we've had computer viruses, worms, and other malware; we've had hackers, crackers, spies, criminals, and semi-competent people flooding the Internet; we have people not just making accidental requests but fuzzing and fusking to try to break things or bypass controls.
It's a great principle for the human stuff, but it feels really outdated for technical stuff.
I agree, Postel's principle makes a lot of sense in context, if you view it as a bunch of mostly good-faith people attempting to bootstrap communication in a new medium. Then it's clear that to get things working, you want to forgive errors on the receiving side (to the extent you can do so), but send as clean and unproblematic output as you can. Basically what a sensible, not-anally-bureaucratic human who's trying to establish communication would do. It was also, iirc, influenced by some of the difficulties ARPANET had experienced in getting different implementations to interoperate. But it may make less sense today.
Since then we've had computer viruses, worms, and other malware; we've had hackers, crackers, spies, criminals, and semi-competent people flooding the Internet; we have people not just making accidental requests but fuzzing and fusking to try to break things or bypass controls.
It's a great principle for the human stuff, but it feels really outdated for technical stuff.
[1] (http://www.ietf.org/rfc/rfc760.txt)