Because "gentext" is based on the document type, it would be assumed that the gentext is identical between two documents since they would both have to be the same doctype in the first place.
This concept is the reason behind not "checking" gentext for differences. Any gentext generated as a result ofcontent or attributes would be flagged as different, not because of gentext, but rather the content and/or the attributes.
Like Ed said below, you could create PDF's of the two documents and compare that, but if you have a large difference... say a paragraph was added... the PDF's will now be "different" from that page on. That is often difficult to figure out.
Hope this helps,
In Reply to Ed Benton:
You could compose PDF of the two documents and use Adobe Acrobat to compare the two PDF files. The exact sequence and names/locations of menus and menu selections varies between versions of Acrobat, but I think that anything version 6 or higher has the compare functionality.