Do general purpose line of business programs last for decades though? I suspect that the ones that have lasted have gone through enough iterations to the point of being unrecognizable to original authors...
Not just LoB, also EDA software, specialized industrial and automotive testing / HiL software and general equipment control software where you can never start from clean slate because there's existing hardware in old production lines with a 10 year support contract.
I.e. basically everything non-web/non-mobile has a higher lifetime.
Someone on HN said recently that business software is like another employee. You wouldn't fire a senior with lots of domain experience, on whom critical processes are dependent, just because it's time to freshen things up.
Even if it lasts for 5 years, that is still a long time to maintain and so the advice in the book is solid. As a business, you may want or need it to last longer.
I.e. basically everything non-web/non-mobile has a higher lifetime.