a) If i was the owner of the site i wouldn't want to leak PR on every page even if i did like the work that was done
b) If i was the website company i wouldn't want sitewide footer links on sites which make it look like I am paying for sponsored themes
c) if the links are nofollowed, both parties lose, PR is still leaked from the owners site and benefit is not gained for the website company
I think the best solution is a dofollow homepage ONLY footer link. This is the highest PR page, usually the most traffic so good visibility for advertising, you're not creating tons of sitewide links with identical anchor texts, and the owner is only leaking some PR on their homepage.