Is there a component for Joomla that....

Just change your template so that the title is constructed according to your rules. Ignore that!

It's actually set in some code in $mainframe which is defined in joomla.php or mambo.php depending on which one you're using.

function setPageTitle( $title=null ) {
	if (@$GLOBALS['mosConfig_pagetitles']) {
		$title = trim( htmlspecialchars( $title ) );
		$this->_head['title'] = $title ? $GLOBALS['mosConfig_sitename'] . ' - '. $title : $GLOBALS['mosConfig_sitename'];
	}
}

Code (markup):

So, you have some choices

1. you can amend this function and remember to check it every time you upgrade
2. you can write your own function that updates $mainframe->_head
3. you can manually change $mainframe->_head every time

I'd say #2 would be the best.