And by then it's too late and becomes painfully difficult to go back.
Examples: Linux, FirefoxOS. On the other hand, no DRM in HTML leads to the platform still being free.
It's easy to integrate proprietary solutions but it's incredibly hard to remove them. IT is way easier to not adopt them in the first place. In that regard, proprietary software is similar to AIDS.
First, build the infrastructure to support amazing things. (Asm.JS, WebGL, WebRTC)
Second, encourage people to spend real money developing for it, however they want to. (Unity 5)
Third, the open source competitors come around. (???)