It's possible that
some WalMart and Target stores could carry the hobby packs, but usually they only carry retail configurations. One reason is that hobby packs tend to cost more than retail packs because of the chances of pulling scarce inserts. The second is that these stores are almost always by-the-pack, so the moment a box is opened, somebody will have cherry-picked the pack with a thick costume or prop card.
Sometimes a retail version of the cards will have an insert subset that's different from any that are in the hobby packs, but Artbox doesn't do this as much as (say) Topps, where they market 6-pack boxes with a bonus card that's exclusive to each mass-market chain. Artbox doesn't make a retail version for every set they produce; usually the "retail" buyers are kids (or parents who are nagged into it at the checkout counter). The Artbox equivalent has been to sell collector's "tins" with a limited number of packs, perhaps with exclusive bonus cards inside.
Still, some "retail" packs can contain costume or prop cards, usually different from those in the hobby boxes. POA Update had two retail costume cards that weren't part of the hobby distribution. The card companies are quite aware that some people will want to buy boxes of
both types if there's something different inside.
The reason the "World of HP" set is different from the ones devoted strictly to one of the movies is ... Artbox paid for the Harry Potter card license, and they'll produce as many sets as they can get away with, as long as we keep buying them. They really needed to bring out the 3D set before the start of the fifth movie because if they cover only four films, they have a perfect plan for the "World of Harry Potter Update" following Movie 7. A split of 4+3 works a lot better than a split of 5+2. For the same reason they brought out "Memorable Moments" and "Poster Cards" covering the first four films.
Artbox had the license to produce "FilmCardz" and "Action Flipz" for a number of properties, and we would have seen many more of them if they had sold better. The film-cel technology lived on as Cinema Cel inserts for the first few HP movie sets, and some of the technology for the flipz was adapted first for case-toppers and then for the 3D set.
Quite often in the past, cards were shipped almost a month before a movie premiered. That was a good excuse to say you couldn't include some of the best images from the movie because it would spoil it for the audience. This time, the studio made sure that the hobby cards weren't supposed to go on sale until after OOTP started. But the card companies still have a perfect excuse for an Update set, scheduled to take advantage of renewed interest when the movie is released to DVD.
A lot of TV or movie-related sets had multiple series, like 5 of them for the first Star Wars. They did a Series 2 for SW Episode One in 1999. But the phenomenon of a set of 90 cards, followed by an Update set with numbering starting at 91 at DVD time, became a regular thing with Lord of the Rings. It was pretty clear to me that Artbox planned their first Harry Potter movie release (POA) on the LOTR model, even hiring the same card designer to produce a very similar layout and content.
Artbox even put all of the marketing pieces together when they issued factory tins for Lord of the Rings Action Flipz. There were (count 'em) 24 different tins and combinations of bonus cards to collect. If people didn't want to buy a lot of the flipz, maybe we can entice them to buy the tins.
I expect to see "retrospective" sets for Harry Potter for many years after the release of the seventh movie. One thing I liked about World In 3D is that they had a very nice selection of shots that hadn't been on any of the (many) previous card sets.
