One more reason to keep redundancy: keeping duplicate answers adds load only to database and HTTP server (and adds "feature" that authors will update answers, adding points of understanding).
However, deleting duplicate posts is manul-intensive labor, editors will have to evaluate which answer is *the best*, and even then, they might delete it one second after original author updated it to add real "perl of enlightement" - which will be deleted as well.

So select one: ;-)
1 - Micro$oft approach: It is not a bug, it is a feature.
2 - Common sense approach: If it is not broken, don't fix it.

pmas
To make errors is human. But to make million errors per second, you need a computer.