Exactly, people often falsely claim or believe that 'cryptography' some how creates the 21 million cap (people who 'know nothing about programming' seem to be very likely to hold this belief as our friend above dose), nothing could be further from the truth.
It is only the honesty of the mining network (and by that we mean literally just the handful of major pool operators) that enforces the cap. Obviously the high visibility of breaking the cap and the fact that many miners hold many coins that would crash (And I mean a Hyper crash the likes of which would make all prior crashes look like hiccups) provides a huge disincentive, but it's nothing more then an incentive structure, one that gets weaker all the time as mining becomes more of a cartel and margins become thinner.
It's not their honesty though, it's economics. Even if someone could continue mining coins over the "cap" it would be idiotic, because as soon as that barrier is broken, bitcoin loses all credibility and plummets in value. All of the coins held by those miners as well as the coins mined from then on would be practically useless. Therefore, these huge mining pools who are sitting on tens/hundreds of thousands of coins have a very strong incentive to ensure that the cap is stable.
Think about it. What if the US gov said "hey, we're going to double the money supply this year! oh and also, there's a new way to counterfeit money that we cannot detect or prevent!" What would you do? You would trash all of your USD in favor of another currency or commodity as soon as possible.