That certainly sounds nice but it's not true. Or at the very least depends on how you define software. If software is built upon an evolving platform (such as the web) and has a self-supplying revenue stream if it needs one at all, then it can be done and will last.
Even for embedded software though, if something hasn't been looked at for years then the original developers probably don't remember it and may not still be around. If a client want's a feature or tweak then the institutional knowledge is gone and the best bet would be starting from scratch.
