I think it's not that simple - armour can be penetrated or pushed in for blunt trauma, especially flexible armour - but yes, there's an element of truth to that and for rigid armour it's probably a large element. Why do you ask?
D&D basically follows your paradigm - armour makes it hard to hit. TFT follows a different paradigm, that the armour has to be penetrated. Reality is probably in-between. D&D apologises to the other paradigm by damage reduction powers. Some house rules for TFT allow bypassing armour by DX penalty which is an apology to the D&D paradigm.
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David