I took me some time to figure this out:

On flights to HAM, for example, they use Avro, Embraer and Saab. While on Avro service is different between Y and C, Embraer and Saab have the same service for the entire plane. The interesting thing about it is that on Embraer and Saab the entire plane is C-class service with a cold meal. (Only the wine selection is not as good as C on Avro - meaning one swiss assemblage each for red and white.)
So if you fly on a C-TKT, you get C-Class service on any plane. If you fly Y, you get better service (C-style) on Embraer and Saab than on Avro (on Avro it is only a sandwich - like Embraer on really short flights like GVA-BSL). To be complete, on Airbus C has wider seats (2-3 instead of 2-2) and in Y not as good service as in the Embraer, always depending on flight length, of course.