It didn't make sense to me to call the updated G4 look as 4.5, because that was just an update to the look, and nothing else. The old design was getting pretty old and stagnant because it had been around so long. It really needed to evolve to continue to sit on the shelves.
I think it makes sense to call Pony Life 4.5, because I feel like it's obvious it's a inbetweener show/toyline. But I suppose a majority of the community needs to feel comfy with it first.