A complement is a product that you usually buy together with another product. Gas and cars are complements. Computer hardware is a classic complement of computer operating systems...
All else being equal, demand for a product increases when the prices of its complements decrease.
– Joel Spolsky
I definitely recommend reading the whole article. It's 10 years old, but still just as interesting and relevant. Decisions start to make a lot more sense when looking at a company's strategic moves through this lens, especially for a company like Google. They're commoditizing everything from browsers to operating systems to increase web usage so they can increase ad revenue.
I'm not sure how exactly to take advantage of this as an app developer, but my first thought is this line from Rounders:
If you can't spot the sucker in the first half hour at the table, then you are the sucker.
If you're not doing the commoditizing, then most likely you are the commodity. Apps are a complement to Apple's hardware. Driving the cost of apps towards $0 increases the demand for iPhones and iPads. Not sure if this is an intentional strategy on Apple's part, but certainly seems to fit.