Probably a better analogy is this:

Take a car from 1930...it may run, but new cars are safer, more efficient, and have new features. Do you expect Ford to install seatbelts, airbags, and antilock breaks in your 1930 Ford?

From http://digg.com/security/Microsoft_to_release_WMF_patch_at_2PM_PST_today

The differences in OSes go beyond a basic paint scheme. They are different systems altogether under the hood and therefore the analogy to retrofitting a car of yesteryear is probably a more reasonable one.