I would argue the same as Gruber and say that they did create their own format. Whether or not it looks like ePub under the surface is irrelevant, since it's a

I would argue the same as Gruber and say that they did create their own format. Whether or not it looks like ePub under the surface is irrelevant, since it's a .ibooks file, not a .epub. Since it's Apple's format, they can do whatever they want with it without having to worry about how other readers interpret the format. (Unless you mean it would have been easier from their point, in which case I also disagree, since this allows them to use their existing ePub code.)