The "frame=none" attribute has no effect on tables.
The default "topbot" formatting for tables is fine in most cases. However, I have one instance where I would like to use a one-row, two-column table directly below a level 1 section title. This results in two horizontal rules where I would like to see only one. For now I have demoted this title to a level 2, but this makes the section heading non-parallel with the others on the page.