So who loses? Big market playoff shoe-ins - teams like the Yankees or Phillies, who nearly always make the playoffs, don't want to see more competition in their way; fans - the more diehard, nostalgic fans see this as an affront (just as they did with the advent of divisional play in 1969 and the Wild Card in 1995 - fans always pine for the good old days, which tend to be whatever was happening when they became a fan).
You can see why the expansion will always win out: most of the beneficiaries are backed by the potential for big bucks, while the losers don't have much sway - diehard fans aren't going to boycott the expanded playoffs in large enough numbers to make up for all the casual fans who will find a one-game playoff infinitely more exciting and digestible than actually paying attention for 162 games (we should face it, as a culture, we love the potential for heroics and heartache in a high-stakes situation).
I actually like this new format (I know, I'm upsetting you, but hear me out): yes, one-game playoffs are inherently unfair, as any fan knows than an inferior team can beat a superior team in one game. But the format SHOULD BE UNFAIR to a Wild Card team who, by definition, is not as good as the Division winner. [I'd actually much rather see a balanced schedule, but that's a rant for another day.]
The fact is that this will make winning the Division actually mean something - and it hasn't for quite some time. Teams with the Wild Card locked up have coasted through September for years now, resting up their regulars and rendering the last month of the season essentially meaningless (thus cheating fans who buy tickets). Under the new system, teams will want to avoid a one-game playoff at all costs, and will play meaningful baseball for longer.
At the end of the day, Major League Baseball is a business, and they will do anything that makes them more money. Playoff expansion has been profitable (in every American sport) every time it has happened. So love it or hate it, it's here to stay.
[And yes, I actually get college credit for discussing these things every week. Last class we discussed playoff expansion, Linsanity, Tim Tebow, and Teddy Roosevelt. I love you, Trinity College.]