When Keith said applications, I think he meant purpose-built devices. It's more clear in context. We can substitute as follows:
"how many [of the mobile systems, media devices, and in-vehicle embedded systems] care about [graphical] network transparency...?"
As for me, I'm not sure that I need the Android calendar app to be able to display its output on a remote display via X11 protocol or something similar. Instead, I'd load my google calendar elsewhere.
I don't need the Android music player to be able to display elsewhere, because I'd simply load my music collection elsewhere using a separate device, separate application, and separate network protocol.