#1 - Age of the shutter. The old Seikosha shutters from the chrome series are very hard to find parts for these days. The newer Seikosha shutters aren't THAT much easier, but you can still get some parts.
#2 - The black lenses have much better lens coating. Not that big of a deal IF you are careful to use a proper hood and keep the sun off the front element.
#3 - Resale value.