Why does JetBlue have aircraft registered in Germany?
I am the pilot who delivered this aircraft on Friday.
The German registration remains on the aircraft up until the time we (JetBlue) purchase the aircraft. Prior to transfer of title, we perform a series of ground tests and flight checks.  This is all accomplished while Airbus still owns the aircraft.  Once any discrepancies are corrected, and we accept the aircraft, we buy it, the ownership changes and the temporary (German) registration is removed. This is typically the day prior to ferrying it over to the US.
As for the Hamburg/Toulouse question- TLS does not produce A321 aircraft, so all of our JetBlue deliveries come from either Hamburg or Mobile, AL.