Yes, if they (the enemy: Romney, Inc.) spent millions and billions and all that went unanswered by Obama, then they would have the advantage and win. If one side has 1 billion and the other side only 150 million, then yes that will be a problem.
But then you get to a saturation point where simply spend, spend, spend, more, more, more will not really do any more good for you. There is a diminishing return point at which you have gotten all of the bang you can for the buck, and more bucks will not matter anymore, so long as the other side is spending an amount that keeps them competitive.
Also, Obama is the president of the United States, and has all of the incumbency advantage and with that an ability to get free media that only the president can get.
Nor have we even addressed the Moneyball strategy of spending your resources efficiently. Obama's team is doing that. The Romney team's answer is just spend, spend, spend, more, more, more. The Romney people may well be doing the Cold War strategy, thinking they are playing the role of the United States, only they may find themselves playing the role of the California Angels in the 1980s: lots of spending on pricey stars (Bobby Grich, Reggie Jackson, Rod Carew, Bob Boone), and no World Series to show for it.
This is all a complicated argument to make, and maybe I didn't phrase it very eloquently, but hopefully you can figure it out.