The argument for NetBSD is that it runs on almost anything that was ever produced. That isn't the case for Linux, even older x86 is no longer supported in the mainline.
Linux (the kernel) may have been ported to more machines and architectures than NetBSD’s kernel, yes. But is all the code present in the same source tree or do you have to go find patch sets or unofficial branches?
More importantly: is there a modern distribution that builds an installable system for that platform?
The special thing about NetBSD is that you get the portability out of a single and modern tree for many more platforms than any single Linux distribution offers.
