[cmrdporcupine]

I think the parent's comment was more along the lines of: just because an embedded device _can_ run a Unix doesn't mean it should have to adopt the semantics and history of the *Unix environment that POSIX mandates. In particular the model of TTYs, filesystems, Unix-style file/IO, Unix-style virtual memory / mmap, etc. It's not that this stuff is expensive on modern embedded systems (which as pointed out often have the hardware capacity of high end systems from 20 years ago), it's that these capabilities are either not needed, or impose a conceptual model of what a computer and operating system have to be that don't match up to what the machine is designed for.