Sorry about the late response,
Proof to the pudding, so to speak, for this type of practive goes back to the ODBC models that all of your modern day websties use.
Having one central connection allows you to control access while guaranting preformance. If you need data in a large scale form, you usually implement application servers to cache and give performance enhancements.
Hope this helps
Dave -- Saving the world one node at a time