Percentages set "minimal" width, but actual width could be larger because of content inside cells.
For example, at
www.redstaindesigns.com/clients you have a menu (ul-list) in left column, but menu items have "white-space: nowrap;" rule. You can fix it by "ul li a {white-space:normal}" in css/custom.css in template, but you have facebook iframe in the right column that has fixed width of 300px.
As to me, I wouldn't use table layout on mobiles at all. You could make different layout for mobile with
Mobile Content plugin.