Well, in Apple's case, it's because having e.g. Netflix available on iOS devices makes people more likely to buy their very-expensive hardware. If people couldn

Well, in Apple's case, it's because having e.g. Netflix available on iOS devices makes people more likely to buy their very-expensive hardware. If people couldn't get the assorted free service-client apps on iOS, that'd be a problem for Apple. Even with the store metaphor, "loss leaders" to draw people in so they'll spend money on other things are a popular technique.