LoL, I mean, it's a stupid idea. There is no logic behind it. It's just plain bad business. Look at it this way, the game is probably gonna suck. It's being made by a company with a rich history, but has never made an MMO before. Now it'll only be sold on one platform, and you can bet the hard copy will make you install it.
Also, to limit the amount of places the game can be purchased is stupid.
On the other hand, Steam did this at first with their titles. But you see them move away from that business model by putting them on consoles like they did with Portal 2.