I definitely know that the presidential limos are flown in from Washington. They´re in the jet that lands prior to AF1. And regarding Marine One - I don´t think that they have such a heli in a European US base. I believe they have flown it over the pond, too. Unbelievable, the enormous expenditure.
It seems an enormous expense, but I would guess that it's done for security reasons, in case someone might have tampered with a vehicle in another country.
IMO, it is always a priority to keep our President alive when he travels abroad. They must deem it necessary to have U.S. vehicles travel with him.