I'm fine with the house rule to skip the roll, and I've often skipped it in the past. . .either on purpose, or just forgot.
And there isn't a difference between the attacker fumbling and the nearly helpless defender getting lucky - if the attacker fumbles, the defender has definitely gotten lucky. It is all in how its described.
And, if we are both waiving around "4' pieces of cutlery" - you offensively, me defensively, then it is up to you to stab yourself with either my sword or your own. In other words: I only got lucky because you got unlucky.
The first difference comes in to when you have a 6" piece of cutlery and I have a 5' piece of cutlery, so my accidentally slashing you is generally far worse than you accidentally slashing you.
The second difference lies in the fact that my "wild swinging" +0 attack is actually far more dangerous to you almost always, than your odds of self inflicted fumbling. . . .per the other thread, the math odds of random +0 slashing are far more dangerous than the probabilities of a fumble:
http://www.ironcrown.com/ICEforums/index.php?topic=11116.0
A +0 attack is far more dangerous than the fumble. . .as in "There's a 3% chance the attacker will fumble, but there's a 30% chance that the flailing +0 attack will connect." (The odds vary in every instance, but only in very rare instances is it not true that the +0 roll isn't at least a factor of 10 more dangerous than the likelyhood of a fumble).
So they're not really interchangeable, I can't really gut believe that something 1-8% likely to cause you to harm you is = something 20-80% likely to cause me to harm you.
If you wanted to dump one of them, the one more likely to actually change the results of the event would be to drop the fumble chance for the attacker, not the wild attack odds of the defender.
OTOH, dropping the "wild swing" +0 OB attack lets you skip a roll, so it saves a bit of time, I can see the benefit there. . .but while I can see the advantage of skipping it to save time, you're not skipping something irrelevant that only GMs who think the RAW are sacrosanct would bother with, you're actually making it much safer to attack combatants who are stunned (be that stunned PCs, or Stunned NPCs). . .like, if you know they're stunned, never bother parrying and pile into them at full OB. . .it's not like they can hit you.
That being the big change. . .you don't need to worry, so you don't put any OB into DB "Just in case". . .without risk you go Conan on my stunned character and full OB. . .it's not pedantic, nit picking, RAW worship or such, it's shifting almost all the risk from the attacker to the stunned defender. . .and if combatants have any way of telling when a target is stunned, making it a gimmie to go for it and full OB their head out of the park.