As far as I am aware the name of the port is not mandated by the spec. However, it does seem like many portal offerings hardcode the WSRPBaseService name for the Markup interface since this is the name used in service definition example on the OASIS website. To address this issue, I have changed our port name to WSRPBaseService. That change is in the current CVS version.
To make that change in BETA 1, you also need to edit jboss-portal.sar/portal-wsrp.war/WEB-INF/webservices.xml to replace WSRPMarkupService by WSRPBaseService.