JMS Specification: QueueRequestor and TopicRequestor are not interfaces

JMS Specification: QueueRequestor and TopicRequestor are not interfaces

Can anyone explain why in the JMS spec (both 1.1 and 2.0)
javax.jms.QueueRequestor and javax.jms.TopicRequestor are a classes and
not interfaces?
Almost all of types (connections, sessions, destinations, messages etc.)
in the JMS spec are interfaces which makes sense for me since the spec
only defines a generic interface and let the JMS providers implement the
instantiations. Only the Exceptions are classes (which also makes sense
for me) to simplify implementations.
But only javax.jms.QueueRequestor and javax.jms.TopicRequestor doesn't
follow this convention. This makes it more complicated to mock it in unit
tests.
Does anyone know the reason for that?