I think you misunderstand what I mean by "theory" and "theoretical background." Knowing how a computer works from the silicon level up to the operating system helps you design systems, and starting with that foundation helps you build better systems. You can get the same experience after a theoretical education, but you can't fake a theoretical basis from simple experience. You're right that you can learn it, but in my opinion, having the theoretical foundation is key to getting the right type of experience, and also helps you immensely along the way.

All I know is that I look for it when hiring. A Berkeley, Stanford or MIT CS student has a very high weight. They still have to prove themselves, but they definitely have a head start in my book.