The reason that your out-of-state paperwork trick works is because you are:
1. Taking it to a cooperative Notary and Tags place (Runkle's or Brimmer's)
2. The Notary includes copies if the originating state's vehicle code that states the non-titling status there
3. You have a legitimate receipt (sometimes notarized) from the seller in the other state
4. They charge you their fees
I'm telling you all...do this now while you can. Mopeds and Scooter regulations in PA and other states can get reviewed and changed at any time. I persnally think with the latest increase in small 2-wheeled vehicle popularity it may spark at least some upgraded registration fees in the near future, if not a whole revamping of inspection and insurance requirements.