I'm happy to believe that a good game can be made for $4m. My worry is that most good games made for $4m start out with a projected $3m budget...
Feature creep and an 'unexpectedly' (it's always unexpected, somehow) long bug fixing phase are eternal bugbears of the industry.
Talking of which, I don't believe this game is going to be released in 2014. I trust Obsidian to get it done, but I think 1.5 years is optimistic given all the stretch features.