Re: "Roddick moves up rankings despite not playing" - Idiotic article!
ATP should enforce a rule here. If a player retires from a Commitment position, he should be forced to notify the ATP and should be taken out of the rankings immediately. But ATP should also make this public so that everyone knows it before the next Monday's rankings are out.
Otherwise no, it's impossible to keep track of all retirements, even if a player was famous. For instance, Ferrero is still in the rankings, somewhere below #200. He is not entering any tournament and not occupying any mandatory place (for he has not announced injury, so he does not have a protected ranking), so he can stay there until naturally dropping out.