It might be true in case of the Linux kernel, but I think that most software that one is using is made of many many FOSS libraries. Imagine that all libraries and compilers are either from the OS vendor or proprietary. We would see much less software. People may not run servers, but they are surely using the software running on them - same thing applies. Android has much more FOSS than only kernel, and I'm not talking about AOSP.

Chrome, Safari, OS X, Firefox are standing upon millions of lines of open source code.

Now FOSS is at least a crankshaft of software world. Even if that would be all there is to it, you couldn't say that it doesn't matter.