What can WebServices do that EJB can't?

Interoperability comes to mind (MS/Java).

Also, with EJB you need to distribute EJB interface, with WS you got WSLD (I know there's EJB extension for WSDL, but I'm not sure it's used).

Anything else?

EJB is mostly about a programming model for how you implement callable Business Logic. You code is running in a container which looks after management, clustering, transactions and security. Your component can be called by and number of different mechansims including local Java Calls, RMI/IIOP for remote invocation and also Web Services, so yes your EJB can indeed have a WSDL and be callable fro other non-Java envrionments.

If you start instead from the point of view of having a WSDL, which probably will specify SOAP/HTTP, then you are free to implement that in many different technologies, and of cource invoke it via that specified protocol, which very many different clients can use. The big question is how easily you can deal with those quality of implementation issues - your chosen implementation environment may give a lot of help or leave a lot to you.

Summary: you're not really comparing like-with-like. Web Services is very about the interface, EJB very much about the implementation.