this is just an idea i'd toss out there that people seem to already know about but haven't really formalized. besides the in-game resources, the one last thing that seems to limit what a player can do is his attention. this is more or less rated at APM but it doesn't cover the entire picture. some units seem to be especially made to require more attention to take care of than others. thus, a high-APM player won't necessarily do better in a battle than a lower-APM player, simply due to unit composition. the 2 most obvious ones i've seen so far are the Brood Lord and the Carrier. both of them spit out little minions that attack. due to the way the AI works, even if you focus fire on the main body, after one shot the units will switch and auto-target the interceptors and broodlings. if you really need to destroy the main body, you have to constantly click on the body. the brood lord has an additional bonus in that it messes up the pathing of ground units, making it even harder to target the body. roaches are another one- it takes more micro for the opponent to win a battle against roaches, due to the armor and regeneration. some units require more attention from their owners- this is especially true with terrans. cloak has to be manually activated, tanks and vikings have different attack modes, marauders are best utilized with kiting + concussive grenades. spellcasters for all races do this, of course. this is probably one of the biggest reasons why players generally don't mass up spellcasters, costs aside. i've seen games where players DO mass up sentries or high temps, but it requires a very high APM to use them effectively. not just units, either- buildings too. warp gates take more timing for the players than other production buildings, same with terran orbital commands. tactics as a whole can also have huge differences in attention- a quick reaper raid can cause a player to watch their borders more carefully for a while even if you're not planning another raid. even setting a bunch of waypoints on your scouting worker doesn't take much effort on your part, but it does mess around with a player trying to get it out of your base when it's randomly changing direction all the time. i dunno, should there be some (unofficial) "attention" or "micro" rating for units/buildings? i think this is one of the biggest reasons why a simple APM rating doesn't really distinguish actual effectiveness in-game.
I wouldn't be surprised if Blizzard already considers this. You list a lot of examples, but they are just that, examples. The complete picture is much, much broader. If you don't think lings and roaches require a lot of micro to use effectively (not saying you do, just noting they are unlisted) then you aren't using them right. I've heard about the thing with carriers/broodlords. If that is how it works (I've never seemed to have a problem with it when fending off carriers as zerg) then it sounds more like an AI bug that needs to be addressed, not a game balance issue.
You can take this one step further. With certain build orders you can force your enemy to build units that require higher APM to be efficient in order to counter you. If a player is known to be more macro oriented or has a lower APM cap this method can be incredibly efficient. I've heard it referred to before as "APM harassment."
