I agree with you on Google. They are first and foremost a media company and they have at this point (with the recession, slow down in advertising revenue, possible upcoming competition with Microsoft/Yahoo and a decreasing stock price) other fish to fry:)
Also On Demand ERP for SMB is a very competitive landscape with the likes of NetSuite, the upcoming SAP Business ByDesign and many other firms with a formidable mindshare and headstart.
Finally most accountants are very careful about where they place their financial data. Brands like Intuit, Peachtree, Netsuite etc have spent years building up trust and even though Google is well known would be an unknown entity as far as accountants are concerned.
BI Publisher has turned out to be the type of product that can be extended and put to uses that were never thought of by the original developers.
Whats nice about Tims blog is you from the early days of his blog to now see the progression (from the early XML publisher days) of BI Publisher from just a reporting tool to a full blown ERP reporting system.