Conspiracy theory.
What's to prevent someone from charging the iPhone when they get home? Seems cheaper than buying a second device. I have an iPad, yet I normally charge the iPhone when I get home - I use my iPad when I want the iPad's size or other capabilities, not because it's the only thing charged.
Other cheaper solutions: Accessory battery (like the iPhone Smart Battery Case, or the Mophie cases). Reducing display brightness.
Besides, if people are dissatisfied with the battery life of their iPhone, will their solution to be to go out and buy another Apple product? People buy additional Apple products only because they have satisfactory experiences with the Apple product(s) they already own.
Here's the thing about battery size. It doesn't just matter how big the battery is, but how the device uses that battery. Apple's solution has long been to deliver the same battery life as the competition with a smaller battery - greater efficiency. Now, they could have chosen to deliver longer useful battery life by putting in the same size batteries as the competition (to go along with the enhanced efficiency). They haven't, because they have good reasons to believe many customers appreciate having smaller/lighter devices in their pockets (and backpacks/briefcases).
Now, smaller batteries also cost the manufacturer less money, so Apple may make a better profit on each device (or put the money into other components). So in that sense, this is a classic case of the "Capitalist Conspiracy" - making more profit at the expense of the consumer. But the Capitalist Conspiracy only works when the customer buys stuff. Again, if they're seriously dissatisfied with the product(s), they may never buy that company's products again.
My theory is that Apple knows that most consumers already consider the battery lives of their devices to be "sufficient." There will always be those who will want "more power." Based on the comments I read here and elsewhere (and my own personal experience), the "more power" crowd can never be satisfied. No matter how much power you give them, they believe their needs are even greater. "Off the shelf" is never good enough. It's part of their self-image. The only conspiracy is that Apple's designers and marketers hold meetings and decide that they're not going to give the "more power" crowd everything that's on their current wish lists.
That would be like, trying to wipe out Apple in favor of the competition.
