NFC is becoming prevalent in Android devices right now, even though we haven't started seeing too many companies adopt the use of NFC for payments, or any other kind of use that could be done through short-range wireless communication. The new Galaxy S4 looks like it will have NFC built into the battery, just like Galaxy S3, and unlike the Galaxy Note 2, which had it on the back cover.
The battery itself seems to be rated at 2,600 mAh, which can be deduced with a simple formula (mAh = Wh x 1000 / V). This is larger than the Galaxy S3 battery, which was rated at 2,100 mAh, but smaller than the Galaxy Note 2, which was rated at 3,100 mAh. The Galaxy S4's battery seems to be exactly in the middle, which is not bad, although I would've still preferred a 3,300 mAh battery or larger. If Motorola can do it, so can Samsung.
Perhaps Samsung wanted to make Galaxy S4 thin enough, even though early reports say that it may be thicker than the Galaxy S3. I don't think 9.3mm, which is what the Droid RAZR MAXX HD measures, is that thick. It's also the thickness of the iPhone 4 and iPhone 4S, and many tens of millions of people seem to have been happy with those.
Of course just using a bigger battery shouldn't be an excuse to make the software and the chips less efficient. Those should also become more and more efficient in time, not less. And after they handle that, then they can use a bigger battery to help most people reach at least 2 days of battery life, which is how things were before touchscreen phones.
The goal shouldn't be one day of battery life for most people, because that means the people who are more active on their phones than most, the professionals, would experience much less battery life than a full day. That's why Samsung and other manufacturers' goal should be to give one full day of battery life even to the most active users. If that ends up being two or three days of battery life for everyone else, that's just a very nice bonus.