Only that it has been specifically said to make it easy to figure out what is minions, KD. Much like it has been said to make it easy to figure out that a monster has an aura around it. Avoid "gotcha" moments that are antagonistic to the players.
I guess this is the crux of the issue.
I don't see where a player using an Encounter area or close power to take out a bunch of minons or even using a Daily area or close power to take out a bunch of minions is the DM being "antagonistic".
If a player was bothered by that in my game, I'd ask him what the big deal is. It's not as if the Encounter or Daily power is lost forever. With 4 minions and 4 standard monsters, didn't he just wipe out 2 of the 4 minions (or even wipe out one or more minions and hurt some standards)? 10% of the encounter is wiped out with a single power from a single player. If every PC were capable of doing that, the encounter would be over in 2 rounds and would save a lot of resources like healing surges.
Stunning the PCs is a lot more of a gotcha and unfun than this and more than 10% of all creatures can stun.
There is one purpose for minions and one purpose only. To increase the number of foes so that the players can wipe through a bunch of them in an epic-like battle. If minion battles are supposed to "appear" more threatening (e.g Orcs inside Moria) but not really be more threatening, where exactly is the thrill of that threat if the DM states which foes are threats and which are not?
The DM has two options:
1) Tell the players which are minions (and hinting at it is for all intents and purposes the same as outright telling) so that when any non-minions show up, the players also instantly know that they are not minions and there is no surprise or scrambling to change tactics or anything. (Note: the DM should mention when obviously different creatures, race, weapons, whatever, show up).
2) Do not tell the players which are minions and let them figure it out on their own gradually so that when any non-minions show up, the players do not necessarily know that they are not minions and there is surprise when the Scorching Burst doesn't even slow them down. Opps. We thought the Wizard and Rogue were covering that flank, but guess what.
I just don't understand the concept of walking through encounters with a boatload of knowledge as being considered more entertaining than the alternative. It's not that the PCs should have zero knowledge, it's that they shouldn't have metagaming knowledge like which foes have 1 hit point. No more than they should know which foes have AC 17 and which have AC 22 if both foes are in chainmail.