While MIT prides itself in admitting students with passion and interests over those with 1600 (I suppose 2400, now) SAT scores, I think that the truth is that the overwhelming majority of the students who admitted are still the type to overachieve, overcommit, and - most importantly - follow the rules. To get good grades in high school, you turn in all the assignments, complete tasks (as inane as they may seem), and take the tests.
What this turns into, from my experience, is a large set of students who are not natural risk takers. What's more, I'd argue that MIT makes it or made it difficult to take risks and explore on your own. They load you down with work, pressure you into taking on a UROP (undergrad research for the uninitiated), and it's a rare student who has a significant project on the side as well.
In contrast, places like Stanford seem to encourage thinking outside of the box / trying different things. Their culture definitely doesn't seem like it slants toward loading yourself up with classes as a badge of honor, and I think that's a hugely positive effect on the ability of students to find time to dream. It feels like a cop-out answer, but I've finally admitted to myself recently that this east coast - west coast cultural divide (see inmygarage, above) does exist, and is incredibly influential.
So while the students who have left MIT and become successful are well-known and, frankly, represent, their reputation is disproportionate to their number. You don't see* MIT sophomores walking around handing out business cards for their "startup" - and I don't think it'd be such a bad thing if that changed.
* in comparison to other schools