I do not know much about the bullet, I'm starting to study it now ...
In a view from outside, without knowing its architecture, as used in the application, I saw a game engine as a software component (CBSE) ... but studying it better, mainly as used in the application (dependence of the source), I was not sure about that.
The Bullet Physics Library, and others game and physics engines, can be considered as software components? (CBSE - http://en.wikipedia.org/wiki/Component- ... ngineering)