If it's part time, you have some control over your hours. If it's full time, you generally show up at 9 AM and not 7 AM.
No homework. Not only is this "less work", it means you can forget about it when you leave.
You get supervised insofar as it's needed to make you do work (or, to be fair, insofar as it's needed to make the average job-holder do work). You don't get supervised because you are a "child" (even at age 18!) who "needs supervision".
The work you do is useful; you aren't just digging holes and filling them back in.
The work is (usually) much more objective. Even for a janitor, either you clean the toilet or you don't. The sole criterion of most schoolwork is pleasing the teacher.
The status gap is less, and most bosses do not make you do displays of submission all day just for the sake of humiliating you (although I admit some are indeed like this).
Your co-workers generally either hang out with you (if friendly) or ignore you (if not). They are usually too busy to spend all day being evil to you for the sake of being evil.
Even menial jobs usually have some path to promotion, while a super-genius student is treated identically to a dumb, lazy student.
You aren't semi-forced into swearing a loyalty oath every morning.
You aren't forced to sing propaganda songs, or systematically lied to to favor the interests of the current politicians (see http://www.paulgraham.com/lies.html).