In response to my presentation, Mark Birbeck pointed me to this post claiming that RDFa is usable within XHTML 1. 
Technically, it may be. I've written up some code based on Mark's example, using "dc:title" in a @class in a div. It validates as perfect XHTML 1.0 Transitional. 
But if you use 'namespaced' classnames, you cannot style the class. You can style "dc-title", but not "dc:title". CSS compatibility is something that we should shoot for. eRDF and non-namespaced class names can be styled, RDFa class names cannot - yet. 
