I suspect there has to be some reason for why they are doing the release like that, because this seems unprecedented to me.
Maybe the number of copies is very limited. Of course they could have explained why they suddenly change their release strategy for a book, but then that would be out of character. I think it might also be because they already released the regular edition.
Remember, when the article for the Special Edition first went up, there was no mention of this store only purchase plan, that is something that they decided on later.