This is just dogma uncritically repeated by the FOSS crowd. Is it true? No. Unified chat on all Apple devices (via iMessage) is a huge competitive advantage for them. It's already far better than decent, and I really fail to see why opening it up would make it any better. FaceTime also works better than Skype, which is amazing considering how much of a lead Skype had at the outset. In short, I struggle to come up with a single fact which supports your assertion.