Now that's a bit far fetched, no? Ever thought about that Blizzard got tired of hunting down cheaters/hackers and shut down their accounts? Not to mention constantly issue patches because some funny hacker screwed up the whole online infrastructure because Blizz decided to make everything open? Why even bother with these people? That's like trying slapping a NDA on the Diablo 3 beta in an age of youtube, facebook, and "You are connected" age.
Not even worth it.
And LAN? Who even uses that today? LAN used to be cool, like 10 years ago when internet speed used to be a lot slow(er).
This is scary, I actually agree with Morgoth on this issue.
Enabling LAN would COMPLETELY negate the online DRM, and since it's going to be only DRM for D3 that would be bad. Pirates can play any game with LAN over the internet using software like Hamachi which emulates LAN over WAN.