What on earth are you talking about? Assembly makes sense in desktop computing as well. Have you ever, for example, watched a video? What do you think powers the codecs, JSX?
Yes, I do know that some Assembly is used in systems programming and other niches where it makes sense. To be clear, I was talking about the phase some of us go through (as amateurs) when we think everything would be "faster, smaller, better" if written in assembly - Python is slow. What about C or Pascal? Wouldn't asm be faster? ... but, as we all realise sooner or later, there's a reason we prefer to code in high-level or very high-level languages, and why pre-mature optimisation can be a real handicap.
I'd assume most are written in C or some other higher level language. Certainly I checked the x264 ( VLC implementation of h264 ) and that is C.