The backs are, as stated, the backs. They are shown here without stickers simply because they can exist in the hobby without the stickers (and since there were albums for the stickers to be placed, the expectation was that the card-like backs would remain).
It is there for collectors to track that part of their collection separately (if they wish). If you're more of a "Whole Sticker" kind of collector, then you should use the base set, as we've attempted to track all the combinations that have been found to come out of the packs.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).