Ok, I was impressed by the Drools-Excel link. On a previous project, we did exactly this: took business rules written in MS-Excel by the biz users, wrote some scripts to convert Excel->XML, and our program worked with the XML 'rules' at runtime. Very nice that the drools people provide a standard way to do this.
I'm stressing the business users because IMHO rules engines are supposed to make biz rules more maintainable. And one way I've see that work is if you can actually take what a business analyst gives you (eg: an Excel file) and convert it to a format that the program can use (eg: XML), with little or no programmer intervention. BUT if the programmer is just writing the rule in XML instead of Java, then... like you said, it's a skillset thing and that leads to other problems (a topic for a long blog entry ;-).