Legacy seems to have become a bad word lately. If you're not running the latest software from (fill in the blank) then you need to upgrade. One software vendor has even portrayed users of their old product versions as dinosaurs.
The fact is, the reason legacy systems are still around is that they still work. Change for the sake of change doesn't make sense to me. Old is not necessarily bad, and new is not automatically better.
Consider for a moment the NASA New Horizons space mission which was launched two years ago in 2006. Last year, the spacecraft passed Jupiter, and in another seven (7) years is expected to reach Pluto. Then, in 2016-2020 it will reach the Kuiper Belt of objects extending beyond Pluto. At that point in time, it will be 10-14 years old.
Granted, NASA's budget is certainly far above what any private-sector company could imagine. But their engineers have proved that it is possible to design something right the first time, and have it work & continue to work for a very, very long time.
There are no service packs in outer space.