I wasn't aware minions were such an XP exploit that they were destroying the system. I mean... what, that 5XP after splitting its death destroying encounter math?
I mean I understand fixing effects that trigger off of deaths so that minions don't break those... but fixing minions so they can't be killed en masse defeats the entire purpose of having things that exist to be killed en masse.
I don't think they are breaking the system, no. But minions are still intended to be part of the fight, and the xp budget reflects that. If I have a group of 5 PCs, and want an even level fight to feature a mob of foes, that might mean 12-15 minions and 2 standard monsters as 'mob leaders'.
Except that with the right auto-damage powers/items/etc, those dozen minions might die almost instantaneously and automatically - or be unable to approach some PCs without auto-dying, etc.
The answer might be to instead bring them on in waves, have them spread out, have them only use ranged attacks, etc... but that can get old when you have only one way to use them in every single fight they show up. And not especially fun with raging orc berserkers minions have to fight the same way as crafty elven archer minions.
The goal for minions is to, yes, be enemies whom the PCs can cinematically wade through en-masse. But it wasn't for them to provide no threat at all - hence why "damage on a miss" attacks don't hit them. "Damage without an attack roll" does, though, and yeah - it feels like an oversight.
I tried out a couple different approaches in a paragon-epic game. One example was to have auto-damage attacks only knock them prone, not kill them - unless they were prone already, in which case it did. So auto-damage was still useful against them, but not an immediate combat-ender. Yet it still left silly situations like a pack of them charging the sorcerer (who had spark shoes) and all getting knocked down when they got near him.
I switched over to the damage threshold system, and it worked quite well. Big damage would still take them out, which felt appropriate. Casual auto-damage did not. And suddenly the PCs had to actually acknowledge the presence of minions, rather than being able to dismiss them entirely.