I've done some searching and here is an example of a fairly semantical theme:
http://turkish.doom9.org/smftheme/index.php?theme=15
It uses a single table to display the board index. However the board index could be considered a table anyway so that's not really unsemantical.
I found it on a site owned by an SMF themer called
Eren who has made some other semantical themes as well. I haven't a direct download link for the theme above though
But I've let a post on their blog asking where to find it, so hopefully they'll get back to me so I can try it out.