Please allow me to bring to your attention the fact that Moodle 2.0 does not work that way. There's been a vigorous discussion on this change at MDL-25718 and I'd encourage everyone to vote for a remedy that is correspondingly equivalent to the behavior we've come to expect from Moodle 1.9.
Gradebook
Viewing grades of expired students
This discussion has been locked so you can no longer reply to it.