That means available number of architectures. NetBSD still support some pretty esoteric stuff, but though I haven't actually counted I would expect Linux to run on a comparable number of architectures.

Now, the kernel will probably boot successfully on a given machine, but whether hardware (i.e. driver) support will be decent enough for everyday use is a completely different matter! For example, NetBSD "works" on this laptop of mine... except for Ethernet card, Wi-Fi card, touchpad, ACPI suspension, external monitors via the docking station, ... :)

I'm trying (for fun) to bridge some of these gaps, but you can see how this isn't appealing to the average user.