You have to factor in equipment and space too. Electricity isn't the only cost to mining. I would think it lower, 3.5 mil, perhaps. And most big mining operation are counting on the continued success of bitcoin to justify initial costs. I think the past months troubles have made some question that.
5,000,000 difficulty @ $15 per Bitcoin would give you a little over 10 % markup, which is still somewhat above where most highly competitive markets settle. Initial costs are only a barrier to entry (tying up capital), and operating costs are typically tackled with economies of scale. Obviously, at less than $.30 profit per day per gigahash, you'd need a giant operation for mining to make any sense, anyway.
The numbers are very rough estimates, of course. For instance, I'd expect serious mining operations to by power in bulk or do something more creative such as start their own windfarms in order to get some cheap electricity...