I find this lack of a residency requirement fascinating, thank you for confirming it. I previously tried to exchange a US licence for a German licence (I am a German citizen) and I was informed I had to have an Anmeldung (registration of my place of residence with the local authorities, and hence likely a tax liability) and had to be living there for at least 6 months. The UK similarly requires at least 6 months of residence before one can apply for a licence.