It depends a lot on the domain and your expertise of the business overall. For example, working for a non-profit is completely different than working on trading algorithms for a hot hedge fund where you also partake in creating the algos.
I just don't think that comparing programmer salaries across the board makes much sense because of the different domains. Understanding the domain is often more difficult than understanding the programming language.
So you end up with salary data, but you have no way to analyze it in any way, for instance to answer "why do some people get paid x and other people get paid y?" So what's the point?
