Hi Luke,
I have to agree that, I'm also one of those who gets confused between RPC vs Document style quite often. But upon lot of discussions and readings, I came to a conclusion that, Document style is more benefited when you have a huge document that can be validated against some schemas and may take a longer time to process. Not necessarily asynchronous, but yes, it may involve lot of validations, parsing etc. This kind of service invocation is applicable in the example you quoted below, where you need to validate the application form against several xsds etc.
On the other hand, RPC is more of quick operations.... say calculator (may not be a good example) but the underlying principle here is use RPC if you think that operation is quick and does not involve lot of validations against the validity of the incoming
SOAP request on the other hand, use Document, if you need validation against schemas for enforcing business rules.
I think this may be the reason why Document style is preferred over RPC in SOAP based WS, as usual business usecases are B2B transactions, which involves lot of business rules to be validated before processing the request.
But I believe, this confusion would still continue for me too