Paul,
although I agree with your article at heart, I also have a feeling that there are other implementations that use SOAP-RPC because other approaches would simply be difficult. Take a look at:
http://msdn.microsoft.com/library/default.asp?URL=/library/techart/xmlanalysis.htm
for a concrete example. This is also in support of the Will Provost's question 1. I'm sure that there are also some distributed apps hanging around which warrant the use of SOAP-RPC because of interoperability and complexity of data passed between the nodes.
As far as Google is concerned, because of relative simplicity of their service, they probably should have offered HTTP/XML interface to the developers as well (account could be also passed in the request header as to abstract the API calls). I also feel that their reasoning for RPC style soap was purely because of backwards compatibility concerns.
you know it's been a looong time since I read that, do you know of anyone that actually uses XML for analysis, it struck me as totally bogus and overweight at the time. Could it be that Microsoft has changed their strategy from Embrace,Extend,Destroy to Embrace,Glut,Destroy?