Nearly every RPG with a d20 attack roll, D&D included, has a 20 being awesome, a 1 is balls. Near misses are usually described as parries or armor absorption, bad misses usually not connecting at all. Now tell me that doesn't sound at all familiar. How to narrate the d20 results has thankfully not been in the RAW, but are you to tell me practice, especially so ubiquitous, has no bearing? I guess you've never heard players lament, or laugh, at a 1 or 2 then.In classic D&D it is an auto-miss, but nothing says it is a fumble. Likewise in 4e. I don't remember any fumble rules in the 3E core rulebooks - were they introduced in a supplement? And when I played AD&D 2nd ed a 1 was an auto-miss but I don't remember any fumble rules.
I have played a lot of Rolemaster, which does have fumbles. It is a very different game from D&D.
We might say, that with a heavy weapon, the strength needed to bring it to bear caused a couple points of damage even though the blow didn't connect, if we want this wankery in our games. In either case a 1 should still miss.
But the WOTC developer said it was an extra well placed blow when he rolled badly. That simply doesn't jive, cat. Hence, the OP doesn't buy the reasoning behind "damage on a miss".
I get the point. It would have been a 19, but the parry turned it into a 3, so to speak. STR damage still results, because big hammer is big. There's any number of ways to narrate the numbers, fortunately.
But this does screw with the internal consistency of d20 results as it's practiced, and there are better rules variants for heavy weapons than this one, that don't cause a major WTF amongst a large number of players.