His demo does not include the "-ms-" code supported by IE10's earlier preview releases because the latest IE10 now supports the updated syntax, so when IE10 launches stable, I assume it will not be necessary to use the "-ms" prefix for radial gradients.
See:
http://www.broken-links.com/2012/06/26/the-new-radial-gradient-syntax/
Peter's demo:
http://www.broken-links.com/tests/newgradients/radial.php
His demo does not include the "-ms-" code supported by IE10's earlier preview releases because the latest IE10 now supports the updated syntax, so when IE10 launches stable, I assume it will not be necessary to use the "-ms" prefix for radial gradients.