The Generations label was indeed more of an after-thought, to differentiate the gimmick toys from the gimmick-less ones (the toys that we'd call "mainline", but with the focus and quantity now being on the gimmick toys, it now makes them the "mainline" in the eyes of Hasbro).
It is also a way for Hasbro to direct the attention of collectors to specific toys, but not go so far that it looks like a different, non-movie, toyline to the general public, who buy the bulk of their products.