I hate to be cynical but it seems like doing this is just saying, "I am more important than the people who send me email, so I will place the burden of tracking my schedule on them." The other interpretation of this is that his email inbox is generally full of useless dreck that does not matter all that much to either him or the sender. Perhaps the success of this experiment says more about the kind of email he receives than it does about the general applicability of the experiment itself.