The point of running the doctests in the docs to to make sure the *docs* are correct, not to make sure Python is correct.  So IMO adding them to regrtest is much more trouble than the tiny benefit it would produce for test coverage.  On the other hand, having 'make doctest' run when '-uall' is specified would be cool, if the tests can thus be run by the buildbots.

But I think should be 'make doctest', and not regrtest using doctest to process .rst files.  The reason is that Sphinx has extra facilities that allow docttests to work without having to have "boilerplate" code in places where doing so would disrupt the narrative flow.  I could be mis-remembering (and Georg will correct me if I am misremembering again :), but I don't think those work when doctest is used directly against the .rst file.