You only have that right in advance, though. If I get an iPhone and buy a bunch of software on it and then 3 years later Apple Changes The Terms Of Our Relationship, I don't have any ability to migrate my data (let alone my purchases) to another platform. Not only do I have to buy a new smartphone, I have to re-buy my apps even if those apps are available on Android. Even if the app's developer wants to give me the app for free on other platforms, they can't, because Apple refuses to give developers any information on their customers. This came up previously when some OS X software had to leave the Mac App Store. Likewise any music or videos I bought on iTunes won't migrate over to my Android phone - in the era of physical media this wasn't a problem, you could pop your CD or DVD into any player you want so you had true freedom.
Windows and Mac and Linux environments are not sandboxed like this either. All my data is files in folders, and I can export it as I like to another machine.