There is at least one major error in your question: In an REST backend the business logic still is on the server. It has to and having business logic in the browser would be pure madness.

From there we can go on and see that the most complex part of any serious web app rests on the server anyway. The browser can only take the View part of the MVC, maybe a few elements from Controllers. Main Controller functionality and especially Model are just to security relevant.

Beyond that: What do you want to write as web apps? If I want to do something smart, I don't look at my competitors, I use Google and StackExchange to find that it was done before a hundred times or at least something similar. There are libraries for mostly everything. The times when keeping your code a trade secret are gone, at least when we are talking about the user interface.

Is it reasonable to use Javascript MVC Frameworks for closed source paid web applications?
What is this variety of kidney beans called in English? We call them "Chitra Rajmah" in Hindi.
http://www.helloorganic.com/Rajma_chitra.html

