Submitting a pull request to fix this
Checkbox behavior works as expected, with a focus class added when tab focus occurs on dom element. The radio button behavior is unchanged, but it (arguably) functions as expected, with the .ui-state-focus being applied to the label, but nothing is visibly indicated. I guess the real question is whether or not we want to show some indication on a radio button set when it's dom element is tabbed to, which would be a divergence from how it works when using the mouse.
Also, had to change the checkbox demo...added a form element b/c the tabbing wasn't working until I did. Also, added a test for the checkbox behavior.
This is my first attempt at contributing, so please let me know if I did something wrong. I read the commit guide a dozen times before I got the huevos to commit.