That hack in particular took multiple months of preparation and was took down by the institute in less than 1 hour; before anyone could really see it. Also the amount of security and possible consequences has increased drastically in the last 2 years; continuing the trend of the last 6 years.
I have some further opinions about what you allude to at the end of your comment, but that should probably be taken offline.
http://hacks.mit.edu/Hacks/by_year/1999/r2d2/
Several Lobby 7 hacks were also left up for a while (though admittedly less obvious and dangerous perhaps than Great Dome hacks).
I know people who were at MIT then. It was, by all accounts, a vastly different place.
They did the annual sodium drop pretty soon after 9/11 and were somehow surprised when the response was different.
For smart people, they could be really, really dumb.