It seems that the SimpleServer and HL7Server are developed or maintained on two separate tracks. I suggest to combine them in order to have less code to maintain but also to create more consistency in the use of interfaces. Eg. make SimpleServer extend HL7Server or the other way around, whatever makes most sense.
This is finally committed and will land in the next beta- The .protocol. and the .app. hierarchies are being merged, with HL7Server being deprecated, but the MessageRouter and ReceivingApplication frameworks being adopted by .app.HL7Service.
Now working on documentation.