The issue is not related to the namespaces. What this ontology is doing is declaring some annotation properties instead of importing the ontology that already defines them.
The reason for doing so is that the rest of that ontology does not conform tho the OWL 2 DL profile, and importing it would make the goodrelations ontology be OWL 2 Full as well.
Namespaces are not limited in ontologies: any on to go can define a class or a property in any namespace. Keeping the ontology prefix synchronised with the entities prefixes is only a convention, not an obligation.