Where is Jonahirt? We need someone to defend EA!
I can play Devil's Advocate if necessary.
From a financial standpoint it'll probably be a good move. Most of the fans of series will still buy the next in the series as long as it has some single player content, and it will open series up to large casual markets the originals haven't tapped.
A focus on multiplayer can greatly extend the life of a game.
Social connection through multiplayer and Facebook can open up competition between friends, with scores posted instantly online for others to see.
Mass Effect 3 had multiplayer and it was still a good game.