TF creates the columns with a table because you cannot build flexible layouts that work well in IE 6. If any item (image, table, form select field, long words) in any of the columns is too wide by IE6's measurement (which is different from other browsers, so everything still looks fine in other browsers) the whole right column will drop way down below the layout and move to the left.
Nonetheless a DIV-only option is coming, because for static width Layouts there isn't that dropping sidebar issue. That option won't come within the next few weeks, but it is high on my to-do list. The reason I started with the table-colgroup-div technique is that it can do both static and flexible width reliably
On a side note, this is a bit more than just "using a table", the layout technique in Atahualpa/Themeframe works with the colgroup element to set the column widths, and a DIV wrapped around everything. Simply using a table would cause other issues, for instance while no sidebar would drop, the table would expand beyond the desired width causing vert. scrollbars whenever it encountered too-wide-elements.
This does not happen with the way I am using both a table AND CSS Div's, which in my opinion combines the best of a DIV and a table
But as mentioned DIV-only will come, was even planned from the beginning...