This is application-dependent. One application may set the green maximize button to make the window fit the size of the foremost document, while another application may set the maximize button to stretch the window to fill the screen, while yet another may set the button to return the window to a default size. The definition of "maximize" depends on what application the window belongs to.
As far as I know, there isn't a way around this. I have seen AppleScripts that let you control the size and placement of Finder windows, but none that were system-wide and could control all applicaitons (as, of course, not all applications are AppleScript-able).
Hey, if you REALLY want windows that take over the entire screen, I can suggest Microsoft Windows -- it's "application-centric," where the focus is on one application... but on the Mac, it's "document-centric," where you can see many documents, even from different applications. My best suggestion would be to try and work the way the Mac works instead of trying to make it work differently... use the "Hide" feature and "Minimize" features as well as Exposé to control your open windows and applications. Trying to find a way to make windows completely take over your screen will only lead to frustration, as it's counter-intuitive and probably just not possible.
Here are some sample AppleScripts dealing with the placement and arrangement of Finder windows and icons -- perhaps you could modify one to fit your needs (these are for the Finder and Finder only, no other application):
http://www.resexcellence.com/applescripts/window.shtml
to Mac.
) can do this, but apps like Safari and others don't.