Sure they can, but the Silicon Valley has an immense human capital in skills, talent and knowledge that you can't find easily in the rest of the world. The type of complexity, the scale of the systems and the engineering culture that you can find in SF is not common around the world. My experience as a developer in an European country is that it is really difficult to encounter engineers with a real experience in developing truly complex systems and companies with true engineering cultures. This is simply due to the fact that the majority of the companies that need that high quality of engineering and are willing/capable to pay for it are based in the Bay area, therefore creating an ecosystem that is unique in the world. Of course there are a lot of exceptions, but I don't think the "they can hire smart developers anywhere in the world" is as easy at it may look.