Every company are determined to build their own walled gardens and tighter integration with their own products. Apple is one of the biggest culprit. While it might result in more proprietary features that better experience the customer's experience, they can exclude users of other products. A recent news in 2014 tells of how former users of iPhones can have their message redirected to Apple iMessenger service if users on other iPhones send a message to their text. This can cause annoyance, especially if one of those emails are important. If you're in one of those camps you can deregister your number through https://support.apple.com/en-gb/HT203042
Also, Apple watches won't work with Androids at all but Android watches work with Apple products. Heck you can find Google products on the App store, but don't just expect Apple to reciprocate.
Also rumors are speculating that Apple are deciding to do away with the ubiquitous 3.5mm audio jack in favor of a single lightning port. I have seen that with old Sony Ericsson phones and their headphones are pretty much useless if you decide to upgrade.
So say no to proprietary software.
