To add to what Peter already said, those functions are part of the Component Life Cycle. Each Flex component goes through several stages during its life. These stages have been divided into small functions, in order to optimize the efficiency of the component. The Flash Player works differently from other VM's. Thefefore, the way graphical components are managed is also very different.
A very detailed paper that goes into the Life Cycle can be found here http://www.developmentarc.com/site/w...cycle_v1.0.pdf
Here's a nice video that explains it in simpler terms, and also describes how the Flash Player works, and how that influced the design of Flex.