I'd have to agree with the notion here that "rules" are not opposed to "creativity".
In fact, it's why we run the system that we do, with a number of additional sources and materials available.
There are a number of rules that have set a very good basis for nearly everything your characters might like to do, and with enough source materials, there exists groundwork for nearly everything.
* We personally, however, limit the "modern" influence of OOC knowledge and IC knowledge. If the setting doesn't have universities for applied thermodynamics, theoretical physics, abstract mathematics, etc, then no, your character would not possibly know what you, as person in just such a society, does. *
The rules are often vague enough and have sliding difficulties to be tailored to unusual requests. With everything that is out there, if you're finding that the rules are strangling your creativity, you're either playing the wrong system (trying to be a theoretical xenogeneticist- try Palladium, Star Wars, Shadowrun, etc...) or you're not looking hard enough.
The rules are there, and they are vague enough to fit damned near anything that would fit what the system is designed for. This is why I look through boards and the only reason I'm interested at all in builds. Not to make PunPun and watch other people (dms/players) cry, but to find a way to play the concepts I have in mind. To shore them up with numbers and see just how far the rules can and will go to support unusual ideas.
Sure sometimes the rules don't work as well as I'd like for concepts, but well.. some things are harder than others...that's fine. They should be, that's part of what makes it a game and keeps me interested. Trying to find new ways to do the concept I have in mind.
If anything, the rules *encourage* creativity, because nothing is so mind numbingly un-creative as being handed a blank sheet with "yes" printed on it.