iPOJO composite relies on the iPOJO Service Context. In iPOJO the regular OSGi bundle context is composed by two parts: the bundle-centric part responsible for a class loading activities and the service-centric part responsible for all service interactions (publication, lookup, binding...).
When an instance runs inside a composite it as a 'local' service context, using a local service registry (the one from the composite). So services registered from inside the composite are not accessible from from outside as they are using two different service registries: the composite's one and the one from the OSGi framework.