And what happens when .Net4 needs changes in order to evolve with the current ecosystem of products and platforms? Or just to run at all? That's right, you're shit out of luck. You go and learn a new tool and hope it doesn't happen again.

With Open Source you can always modify it to fit your needs, long after the original creators stop maintaining it.

I suggest you actually learn the difference between proprietary and open source projects before attempting to continue in this discussion.