If Microsoft creates a store authority for most personal end users, a lot of people won't be able to afford to use the same software anymore(because they can't pay for it). The providers can lower their prices, but we know this not to be the case as they associate windows with big margins. There will be no $9.99 Windows version of Photoshop.
While I'm pretty much against locking down desktop PCs to the point where they become like a cable TV service, I really don't have much sympathy for people suddenly not being able to afford to continue using software they stole to begin with.
Regarding Photoshop, this package is a classic example and demonstration that software piracy really does increase the cost of software. There is no real demand for a Photoshop alternative because everyone just pirates Photoshop. Without a demand for an alternative, the only competitors are crappy FOSS packages that professionals won't touch with a ten foot pole. Without that competition, Adobe has no reason to lower their price. The market has demonstrated that it can bear the price of Photoshop because professionals don't have another choice -- all because piracy of Photoshop has eliminated any desire to have a viable competitor.