JSON is so nice and easy and simple until it needs all those things that made it into XML to get the job done.
I whole heartedly agree, there is nothing sweeter than giving another vendor our WSDL with schema when they ask how to work with our system. It eliminates huge effort and ambiguity in system interaction.
SOAP, WSDL and everything else XML and XML Schema related is overkill for simple interfaces. For complex interfaces it is just - well too complex.
If the time spent creating XML based web services that kinda but not really work (we're only talking interfaces here!) is spent documenting your JSON WS - you get quite a better experience.
Ant this is the reason why everybody has switched to JSON.
JSON has no way to describe in machine readable way what to expect, instead you have to read a document then go hand code the interface in your language of choice.
WSDL and SOAP is not complicated, and I have implemented my own SOAP stack. Then again everyone now days everyone thinks relational databases are complicated.
If you you have tools that implement it for you then there is no excuse.