We wouldn't take this as indication that Steam will start selling TurboTax and the like right away (or at all). We have no idea how long these genres have been visible in the mobile apps, only that people began to notice them last night. They could also be there in error. In any case, we've contacted Valve for more information.
For now, if you want to buy something from Steam that isn't a game, there's always Indie Game: the Movie.
Update: The mysterious genres no longer show up on iOS or Android. Something something Valve Steam vapor.