Why use current Exchange infrastructure rather than starting over?

I proposed an agile approach to improving Healthcare Information Exchange. Why should we keep the current? I covered this mostly with simply "that it is functioning", but did not enumerate why this is such a big deal. Many will say that http RESTful is functioning on a global basis with Google, Facebook, LinkedIn, Wiki, and Blogs. This is true, but these are all monolithic servers. Healthcare is a mass of 10 thousand organizations all with different systems. So Healthcare is special....