All companies with computer hardware and software have a fairly short turn-over cycle. The availability of components is sometimes a factor, and the advancement of software to take advantage of new hardware capabilities renders old code obsolete (and unsupportable). Bugs and fixes are not always practical for old code, and it's not economically justified to fix down-rev code, especially for products that are no longer marketed. Then there's the employee turn-over problem... the newer employees aren't familiar with the the old stuff. In the end, the practical solution is to "sell what you got that works" and offer a trade-up deal.