It doesn't contradict what I said above. Supporting multiple APIs is a burden, whether it falls on those who write their own engines, or those who write those engines for others to use. You can view it as a tax which increases costs and reduces efficiency. The point of lock-in is exactly such tax, which will deter some from using anything else, or at the very least make it more expensive for those who will use something else. This tax is passed to the end user either way, in the form of slower progress, higher prices, unavailability on other platforms and so on.