[drupal-devel] css clear use

I'm trying to develop a theme with floating css elements and there are several uses of clear in misc/drupal.css that are messing up my layout. Is there a particular programmatic reason the use of clear is superordinate to themes? I seem to have been able to override it in the theme css file, but aside from it being temporarily annoying to fix, it doesn't seem like I should have to override Drupal built-in css.