Couldn't Steam pull the game from their shop? Prevent new people from buying it and remotely de-activate/remove existing installs of the game?

Proponants of the walled garden 'App Store' model point out how it's good for users, since it's more secure. Well, is this a case for that? Will the closed app store model step up to the plate now?

Or is the walled garden no better for users, but much better for the sellers of software?