1) Either the log should say "... if jetty-env.xml and jetty-web.xml have been correctly added."
Or 2) it should check if they are there in the war before stating that injection works on servlets.
Or 3) - better yet - the system should be improved so the jetty-web.xml thing is obsolete (like on tomcat).

That log statement was very misleading and it took me quite some time to find out that it was not my jetty6 plugin that was causing the trouble, but that in fact I was missing these bits:
http://docs.jboss.org/weld/reference/1.1.0.Final/en-US/html_single/#d0e5286

I've looked into 3), by adding this in org.jboss.weld.environment.jetty.AbstractJettyPre72Container:

         Class<?> weldServletHandlerClass = Reflections.classForName("org.jboss.weld.environment.jetty.WeldServletHandler");
         Method processMethod = weldServletHandlerClass.getMethod("process", WebAppContext.class);
         processMethod.invoke(null, (WebAppContext) WebAppContext.getCurrentWebAppContext());

But that results in 404, because in org.jboss.weld.environment.jetty.WeldServletHandler#WeldServletHandler
the existingHandler is properly started and the new one is not.