"Do you think that a programmer from one layer can do the same work as the programmer in the layer above?" A programmer can do what he / she is familiar with.

"Do you think that a programmer from one layer can do the same work as the programmer in the layer above?" A programmer can do what he / she is familiar with. You don't automatically know how to build web applications just because you write code for NASA for a living. A web developer who codes in PHP could do the same thing as the NASA coder if he / she were to roughly go through the same path of learning. "What about compensations? Do you think that a kernel developer earns more than a Web developer?" I think you left out the most important parts. I would consider marketing, creativity, luck, people skills, etc to be as important or more when it comes to earnings. You can be the greatest developer but if you don't fit in with the company culture then you don't get a job. Highly creative people might be able to sniff out different ways to earn better than more conventional counterparts. People who are good with other people and communication might be better able to negotiate higher salaries. I believe some of the largest contributors to the Linux kernel are large corporations such as Redhat and IBM. Web development is an industry with a relatively large number of contractors and small web shops, so it's a highly entrepreneurial industry. I would say that anything where you can strike out on your own has more potential for earnings. We could also talk about things like location (developers working for outsourcing shops in India.) How about enterprise vs early stage companies (startups) vs government vs open source? A different person in each of these categories could be doing the same sorts of things but get paid differently. Theoretically the market would smooth these bumps out, but that's not always the case (especially with outsourcing or startup employees working for peanuts in exchange for the possibility of hitting the lottery.) In other words, I think your questions are simplistic.