table-layout="auto" for HTML tables

The FO stylesheets seem to always pick table-layout="fixed" for HTML 
tables. Is there a reason for this? In general I'd prefer automatic layout.

-- 
Elliotte Rusty Harold  
XML in a Nutshell 3rd Edition Just Published!
http://www.cafeconleche.org/books/xian3/
http://www.amazon.com/exec/obidos/ISBN=0596007647/cafeaulaitA/ref=nosim