" Because it is a simple matter for a OS X user to increase the width of their browser on a case by case basis there is never a need to stretch to full screen. The button that most Windows people assume will expand a window to full screen instead, in OS X, expands or contracts to the documents dimensions. In the case of a browser it expands and contracts to the width of the web page.
In windows, there is no easy way to contract a window view. So, rather than jumping back and forth between window sizes a Windows person would just go full screen and stay there."
http://www.forevergeek.com/2006/09/m...ximize_button/
But if you feel you really DO want that maximize button back
http://www.insanelymac.com/forum/ind...howtopic=26669