True, there are odd international edge cases. The Berlin-Warszawa Express (just sold as a PKP service these days I think) is too, but it's a bit more like those TGVs - it's really a Polish service that operates under Polish conditions which includes compulsory(ish*) reservations. But the specific ICEs under discussion aren't really ICEs, they are TGVs in ICE clothing and follow all French norms, from ticketing to catering and everything in between. This was part of the agreement between SNCF and DB for the joint operation, which is a bit like Thalys in concept but unlike that isn't a separate jointly-owned** company.
* Other than the EIP (Pendolino) where there's a fine for not reserving, PKP's setup is a bit like what we do now on IC type routes - tickets are sold with a reservation, but there's no penalty for not having one, though unlike here all coaches are reservable and reservations aren't marked, so not having one leads to an awkward game of musical chairs.
** DB sold their stake in Thalys I believe.