This guy has no idea what he's talking about. Diablo 3 is going to get cracked and you'll be able to play it just fine in single-player, just like any other cracked game. While your character data will be stored online for legal copies of the game, crackers will just hack it so that that data is stored locally instead. Voila, problem solved.
The author seems to be under the misconception that the game's assets will be stored online and then somehow streamed to the player during gameplay. He also doesn't understand the difference between cloud gaming and server-side character storage.