The Magic of the Demons is not COMPLETELY different than our own. It does however seem to be much more, as the old texts say, "OP". They can wield vastly more of it, more easily, and it obeys their mental commands seemingly effortlessly. Because of their vast stores of knowledge they understand better how to twist it and use it, and have unlimited time to put that knowledge into practice.
The only "restraint" they seem to have is that it is THEM. Like a structure held up by the contents, if they are totally drained of magic they will eventually dwindle. This however is extremely rare, much like a person dying of starvation, they do need to go some time without any replenishment.
Because of this, however, they do tend to try and conserve their magic. It is rare for a demon to needlessly waste magic, and humans do that all the time. Our magic comes from the environment around us, so we may as well use it, right?
It is said that humans who have made pacts with demons have gained greater access to their own magic... but this is a path that only fools would take.
-On Magica, writings by Queen Augustine