I imagine that the policy must make exceptions and involve a cost benefit analysis. Any one with Kotka's level of experience must know that many companies don'

I imagine that the policy must make exceptions and involve a cost benefit analysis. Any one with Kotka's level of experience must know that many companies don't rewrite their legacy systems because it is extremely expensive. Otherwise they would do it all the time. You might save in maintenance costs, but the cost of rewriting is much larger. You usually rewrite software when it no longer does what you want it to do, or the cost of improving it exceeds the cost of rewriting. It can certainly take more than 13 years for the scales to tip in favor of a massive rewrite, especially for backend systems upon which many other systems rely.