Sorry about the lack of posts lately. I've been in the web service hell. I think the main problem with web service API is that ideal granuarity of service conflicts with ideal interface for the service.
RPC-style web service API is unsuitable for typical medium to large web applications because too many calls per page has to be made, resulting in unacceptable performance.
State transfer (aka REST) style web service API is typically chunkier (less calls) but message payload could get too big and the reduction of payload size could easily increase payload and client software complexity. What's the point of building a web service API if a complex platform-specific client has to be built to use the API?
While being tormenting, I've been taking my breaks in WoW, grinding through monsters. Oy. I think I was a mule in my previous life.