For a very specific definition of functional that's true. But you can (and many people do) have a functional Linux system without GNU userland, and you could hand a GNU/Linux to most people and it would be practically non-functional for them. Pretty arbitrary line.
Android, last I checked. Also, the vast majority of consumer network hardware (that ain't running VxWorks, at least). Both of these categories of Linux distribution typically use Busybox instead of the GNU userland, and more often than not use an embedded-friendly libc instead of glibc. The only significant GNU component remaining - GCC - is usually counted as part of the distribution's build environment rather than as part of the distribution itself, so it'd be a significant stretch to count it.
