Every time i hear this argument im reminded of something. For a while we had a system that nobody wanted to touch. It was a scary hack done by someone in the far reaches of time. Well one day somebody was bold enough to decide to write a replacement system. They put it into play and did a paralel run. Much consternation was caused by the fact the outputs were different. The developer of the new system however was pretty surprised by this and as such began to do a detailed analysis of the code involved. Turned out the output of the two systems was different because the original system never worked properly in the first place. Well, needless to say the old system was soon replaced by the new system, and lo and behold, much money was earned and much rejoicing was done.
Not that it means your point is wrong, but there is another side to it. ;-)