Why does changing the save settings only work when you do save-as?

I've already set the option to have the files save down to 2007-2009.  However when i open a file and hit save, it saves in the original version.  When i open a drawing and hit save-as, then the file saves in the version that was preset. 

Why can't i set the save version once and have it take affect every time i hit save?