Even though Internet Explorer doesn't support contenteditable on tables that doesn't make it a valid reason for other browsers not to support it there. It's probably just a bug on their side. Having it on tables is very useful.
We support contenteditable on any element, please attach a testcase if contenteditable is buggy on tables.
http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C!DOCTYPE%20html%3E%0A%3Ctable%20contenteditable%3E%3Ctr%3E%3Ctd%3EYou%20should%20be%20able%20to%20edit%20this%20text.%3C%2Ftd%3E%3C%2Ftr%3E%3C%2Ftable%3E confirms that. My apologies.