IDH and DW are the same rules systems. Use the same d100 rolling, skills, talents, and tests/test difficulty rules. How in the good green earth can anyone suggest saying they are similar gives a person, "no leg to stand on." Don't say stuff as obviously incorrect as this, otherwise you lead other people to question your intellignece (advice not an insult).
YES you do have to use the concealment action to be concealed.
Being stealthy is not easy. It takes effort. Thats why it is a half action. That is why it requires the cost of a half action every turn you use concealment. You are not turning on a cloaking device. You are sneaking, hunched over, hiding behind things. If your character is not doing these things (i.e. using the action which specifies he is doing these things) then he is NOT concealed. If you stop trying to hide (not using concealment every turn), you are no longer hiding (NOT concealed). How is this difficult?
You cannot use concealment one turn then sprint in the next turn and expect to, in some rediculous crazy way, still be concealed. This violates the common sense rule on many different levels, primarily: "Some actions are just impossible" [sic]. (i.e. attacking and staying concealed)
Again for the sake of clarity. You conceal yourself it costs actions or slowed movement in narrative, but you ONLY have to test when another character COULD possibly detect you, then you roll opposed perception vs. awareness. If hiding something inanimate you use concealment once and take a test then, any character who could detect it rolls against your roll, inaniamte objects are of course different because, well, they're inanimate.
Ok skimmed the rest of your massive blob of text. Seriously guy, paragraphs… look into them.
I don't know why you mention "getting out of cover to take a shot" multiple times. When did I, or the handbook, ever say this? I did not, I did not even infer it, nor did the handbook. Let me be specific in the hopes you will finally understand how this works.
1 You are concealed.
2 next turn -You spend a half action to continue remianing concealed this turn. You use the other half action to aim.
3. next turn - You take a half action to shoot.
a. Since you made an attack you automatically loose your concealment.
1. What it means is: you've made an attack, that action makes it impossible for you to be concealed until you take an action (do something) to re-conceal yourself. If anyone could normally detect you, or take an awareness test to observe you (without concealment, lets say your really far away) then they do detect you, no opposed concealment tests. You don't move (which would require a movement action), you simply stop being stealthy because you made an attack, thats it. The expanded rules in the handbook are not for "diving back into cover", there is no diving because there was no moving (this is a very obvious premise), attacking is something you cannot do and remain concealed, although you can attack and return to concealment.
2. If your weapon is loud then enemies may use both visual or audio perception skills to detect you or your attack.
3. If you are using a weapon whose shot, or your attack, cannot be detected then the enemy may not test audio perception (can't hear what you can't hear) and can only test visual if and only if he was looking in your direction to begin with when you made the attack. i.e. the enemy detects you when you loose concealment, he does not detect the shot.
4. If you are using a weapon whose attack cannot be detected and no one is looking at your location, or the only enemy is the one you just killed, then no one sees you loose concealmnet, and no one nearby can test to detect the attack. No one sees you.
b. You now use the other half action you have remaining to re-conceal yourself (scooch over a couple inches, pull down a tree branch, pull your glinty gun out of the sun, etc.).
4. next turn - you use the concealment half-action to continue hiding.
Its really not that hard, I just broke it down to a very very very detailed level in the hopes you will finally understand what is being stated. The only thing you aren't getting compared to "first person shooter" logic is the ability to stay concealed while doing full actions (never the rule, RAW or intent of any of the systems, have no idea where you get this idea from) and can be seen if a sniping character shoots something when everyone is looking in his direction. Just wait a turn until the guy you aren't shooting turns his head, then shoot the other guy, same result.
Anyways, thats enough of this. Point, counterpoint, rebuttal; no point continuing to argue now, unless another actual question is asked I'm going to call this topic quits.