Well, first, popups in RichFaces are not loaded at display time. They are loaded when the page loads, but are hidden. The show() method simply takes the panel and makes it visible as an overlay DIV on the page and the hide() method makes it invisible again.
JSF does not concern itself with focus in any event. You should be able to set an "onshow" attribute for the tab and have the code in that attribute direct focus, but RichFaces won't do any focussing for you.
Sometimes the only way things ever got fixed is because people became uncomfortable.