The point is that if you have a homogenous system (all from the same manufacturer, all the same model, all built off the same install disk), you don't have to run the tests.
Does that same install disk include the EXACT copy of perl with all installed modules as production. or was perl and the other modules installed manually on each server?
I understand the theory that they "should" be the same, but that's usually not the real world. Shit happens. I'd much rather find out something is broken, missing, out of place, borked on an install while running tests than when it's in production and I didn't run the tests.
And like I said, I'm not a "always run make test" saint. But assuming things are kosher just because it works on the three other same-OS machines installed form the same disc seems like an accident waiting to happen. THe whole point of tests is to point out problems before they effect production. Sometimes those are tests in the dist. Sometimes they're not. But to each their own.
