Also the complexity is needed when your size goes up. Even verifying that the requests make sense is easier with schemas. Right now there is some project for json-schema going on, but it's not crazy popular yet. SOAP can be self-documenting too with its own structure mappings, type restrictions, etc. etc.
Don't you think it's only delaying the fact you'll have to reimplement the same stuff at some point yourself (since json based rest simply doesn't provide them out of the box)? (yeah - I know rest is protocol independent, so you can have xml and schemas too, but majority of "rest" services just throw some json and hope it sticks ;) - too bad if it changes between versions)