That is a poisonous meme which should be fought tooth and nail. It basically follows the structure of the fallacy of grey¹: "every tool has qualities, therefore they're all fine".
It doesn't account for the fact that some tools dominate others. Meaning, they are demonstrably better in every way for every foreseeable usage. But we tend to cling to our old ways, instead of just saying "oops"² in exchange for new powers. We sometimes even actively try to deny others the very powers we refused to take.
Here, you were very close to make that mistake about svn vs Git/Hg/Darcs. Git doesn't dominates svn yet, but I'm sure it will. Then, subversion will deserve "you should stop using it".
But most often, this mistake is made with programming languages (it's a variation on the blub paradox). And the effects are far worse there.