Honestly PC, and no snark intended, but what is so flexible about 3 different categories (low, medium & high) of damage? I mean I could get behind this argument if page 42 gave some kind of guidelines for creating an effect other than damage (as more often than not players can do damage more efficiently, and usually with a standard bonus effect, by using their powers) but it doesn't. There are no guidelines for adjudicating anything besides how much damage a "stunt" should do. So I am asking... what is so flexible about this?
I'm not Piratecat, but you seem to be operating under a very common misconception. Some people think that because there is only one table on page 42 that it only deals with one topic - which would be the categories of damage.
This is not what page 42 actually is about.
Rather, it handles three
separate things.
1. "The DM's best friend"
This is the good old circumstance bonus of 3.x, just providing a +2/-2 modifier for good or bad situations. This could be clever tricks, useful distractions, particularly (un)convincing lies, and so on.
2. "Cast the Action as a Check"
You have the option of resolving an unusual action as either an attack roll or a skill/ability check. You can pull the rug out from under somebody's feet to knock them prone, throw sand in their faces, maybe even use a scarf to tangle up a construct's gears. Whatever the DM is willing to let you get away with, really.
3. "Improvised Damage"
Based on how devastating and common a source of hurt is, the table tells you how much damage an unspecified hazard might deal.
Part of people's misconception comes from the table, but also the example used: swinging from a chandelier to push an ogre into a fire. This makes people think that the stunt (swinging from a chandelier) causes 2d8+5 fire damage.
It doesn't.
The stunt lets Shiera knock an ogre back 1 square. The damage comes from the fact there's a brazier over there. It's important to keep these two things apart, because the damage would have been determined the exact same way if Tide of Iron had been used to knock the ogre back. The example simply combines two seperate rules into one action, but that doesn't mean that all actions are like that. Some improvised damage comes without using a stunt. Some stunts don't do improvised damage at all.