%{_docdir} can contain all sorts of data, but according to the packaging guidelines, none of it should cause provides/requires to be added to the package. This is a RFE, asking for the auto-req and auto-prov scripts to skip scanning %{_docdir}'s content.
Basically it's a question of executable vs not executable: if %doc files aren't marked executable, no dependencies are collected from them. If they are packaged as executable, somebody might be actually expecting them to work too so it's reasonable that even %doc dependencies are collected too. It's just that the internal dependency generator has some extra twists as shown in bug 234691. *** This bug has been marked as a duplicate of bug 234691 ***