Ever tried to get a <table> to take the whole browser height? Not a trivial task if you want to keep the browser in the Strict mode. Yes, removing
<!
DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
will do, but that's already the Quirks mode.
This css rule will work even in the Strict mode:
html, body, table#main {height: 100%}