Done. No "unavailable" section. That's implementable, but I'm not convinced it's that helpful.
The "available" list is NOT based on the check_reqs scripts; those aren't to hand unless the platform is already downloaded, which it may not be. So instead it's just whether the platform can be installed in principle: ie. whether your platform support it at all.
Therefore, Android and BB10 are always available, ios is only available when os.platform() === 'darwin', and wp7+8 only when os.platform() === 'win32'.