TSA Travel Limitation with Lithium Ion Batteries

I suppose we are going to have to start mailing our batteries ahead starting Jan 2013.

However, I suspect I am much happier with fellow passengers carrying extra batteries in their carryon where they can be reached if they self combust rather than in the mail in the cargo hold of the same plane.

Is their any rationale for this limitation (2 extra batteries over those inside the camera battery cover)?  Or is this another government boondoggle?

Perry