I would say supply and demand. Server-side development has been there for years, many qualified professionals know how to do it. On the other hand, client-side development with HTML5 is rather recent so the talent pool is smaller. You are partly right when you say client-side development is easier: it is easier to start. But becoming a good front-end engineer is probably as hard as becoming a good back-end engineer, perhaps even harder. Modern Web applications like the Twitter are real pieces of software, and developing them is similar to developing *portable* desktop software. So the job market is flooded with people who say they are qualified front-end engineers because they have made a web page for their mom, but when you look for someone really qualified you can't find anyone. Lot of demand, little supply: prices go up. By the way that's also true for mobile applications...