That's a way old question, but I can answer your newer question!
Some stock agencies as well as some commercial printers ask for uncompressed tiffs and even a minimum file size for some purposes. For example, Alamy requires tiffs of a minimum uncompressed size for images submitted to qualify for their progam. I don't think the same requirements apply to images that then get posted on the site, though.
I hate it when I get tricked into an old thread...
I get the tiff conversion, but I was confused by the way it was asked as if file size were the key over everything else.