[jacquesm]

Think 'hospital', certified power, military, off-shore (vessels, platforms, emergency power and so on).

For a system that is bullet proof and where there are very strict requirements it makes sense to spend that money, for your homebrew system it likely doesn't, but you can pick up their inverters for a good discount at the various surplus auction sites with some regularity and that's the best of both worlds: great quality at a reasonable price.