The HTML Scope/Headers Debate
http://juicystudio.com/article/html-scope-headers-debate.php

Lemon, Gez
Juicy Studio
2009

Abstract:

The HTML working group have decided not to include the headers attribute in the HTML 5.0 working draft, as they believe the scope attribute is sufficient for associating header cells with data cells. With simple and most complex tables, this is a reasonable assertion, but doesn't work with overlaid and irregular tables, where the associated headers aren't in the same column or row.