Or it sounds like the mainline client does validation of the protocol message. Perhaps this could be broken out into a library that everyone could use to validate the protocol message before it was sent?
No, it's not a flaw. You can read the chatlog I pasted on page 2 for more information why.
I read most of the post as it was very long.
For the most part I agree with you (I hate bloat as much as the next guy). However, most of the examples you quoted were for things like web servers, HTML, (perhaps I'm missing one). All of these protocols have no consequences for the entire body of people using these protocols. If a web server in china screws up, it doesn't affect me at all. If someone screws up with bitcoin and sends 2 million coins into the darkness, that affects us all. That can only happen so many times before bitcoin is no longer worth anything to anyone in its current form. It would be nice to be able to run a message through a validator to get some indication of _major_ screw ups. This would not have to be part of your script language.