What trains would that be? Street cars and busses are the only ones I can think of that don't have first class. Everything from the S-Bahn and "up" has a first class car or section.
In berlin neither the Sbahn nor the Ubahn has first class. The express trains (RE7, RB14, FEX) to the airport don't either as far as I remember and I don't see one when I check[0]. Similar for many other cities I believe, so I'd wager most travelers the 9e ticket is covering will be on vehicles that don't have first class anyway.
