But, from what you said Tyrlaan, would the three powers you mentioned use entirely different mechanics? Would one power use a percentile check, while another use an ability check while the third uses the target's saving throws? Or, is there one single mechanic that determines whether or not the power attack is successful?
All to hit rolls in HERO follow one mechanic. However the Flash rolls "damage" differently than a standard energy blast (EB) and goes against Flash defense instead of standard defenses. Extra knockback alters the math for figuring out how far someone goes reeling after you hit them, therefore arguably changing the action resolution mechanics. A stat Drain is resolved similarly to a Flash, but goes against yet another non-standard defense.
Figured I'd expand upon it a bit since you're unfamiliar with the system. But I consider it moot because resolution mechanics wasn't my point.
I think you're actually nailing it on the head. To me, if the three powers you talk about use the exact same resolution method, then there is no mechanical difference between the three powers. In the same way, in 4e, there is no mechanical difference between using a fighter's martial power and a wizard's arcane one. They both use the exact same mechanics. The only difference between the two is in the specifics.
To put it another way, if fighter A uses a longsword and fighter B uses a mace (assume 3e D&D for a second), mechanically, there's no real difference. They both use the same attack rolls, they might roll different dice for damage, but, that's about it. The mechanics they use to determine their actions are identical, all that changes is the result.
I strongly disagree with any idea that maintains that you require mechanical diversity, or "action resolution diversity" if you prefer, to have a difference in play between characters. Like I said, most skill based games have no difference between how skill X and skill Y are resolved.
The diversity comes from the player, not the ruleset. My hero uses an ice beam, yours uses a blinding beam. Mechanically, they're pretty much identical (sure, they use different ability scores to determine my chances, but, the mechanics are the same). The diversity comes from the player and how he chooses to narrate his actions.
Your hearing me, but you're not listening. You're defining mechanical diversity solely as action resolution diversity. I'm not. Action resolution is just a small slice of the mechanics pie. Let me try to explain by example.
Action resolution diversity:
Fighter swings a sword; rolls to-hit vs. AC.
Mage slings a spell; potential victim rolls a saving throw vs. mage's spell DC
Mechanical diversity (that's not action resolution):
Bob the Fighter is better with a greatsword than most, in fact one of the best; Bob has Weapon Focus: Greatsword, Weapon Specialization: Greatsword, Greater Weapon Focus: Greatsword, and Greater Weapon Specialization: Greatsword. In addition, he has picked up the PrC Greatsword Pwnmaster.
Joe the Fighter is at his best wielding two weapons, so the greatsword really isn't his thing. Instead he has: Two-Weapon Fighting, Two-Weapon Defense, Improved Two-Weapon Fighting, and the PrC Aragorn Wannabe.
The latter, not the former, is what I'm talking about with regards to mechanical diversity supporting character individuality.
Honestly, I
vastly prefer homogeneous action resolution mechanics. To me, it makes for a much cleaner game and smoother play. And, that's not where you're ever going to find support for character individuality. Action resolution diversity gets you various mini-games from which the player can choose to use at the gaming table.