Because there are other things that don't count toward the daily limit, e.g. +15 for an accept of your answer, +2 for accepting someone's answer, bounties, etc. I've received over 300 on many days mostly because of accepts.

[From the FAQ](http://meta.stackoverflow.com/faq#reputation):

> accepted answers and bounty awards are not subject to the daily reputation limit.

However note that it was recently suggested the wording be made more clear.