And if there wasn't magic in the game system and monsters had all of the abilities of PCs, this math might mean something.
My proof for this is 4E.
Fights aren't fair. Ever. PCs always have a huge advantage.
If one carefully looks at most above same level 4E encounters, they'll notice something. The NPCs often get the upper hand in the first few rounds. A few PCs are bloodied. Multiple PCs have effects on them. Things look dire. But slowly, the PCs start evening the odds and eventually, they start ripping through the encounter. Why is this if the PCs are losing in round one, that they win in round six?
Although one or sometimes even two PCs might be knocked unconscious in an encounter (although most encounters, no PCs are knocked unconscious), they almost always get back up. The monsters almost never get back up.
The three things that cause this to happen are:
1) Options. PCs tend to have a lot of options. Monsters have only a few. Each player can decide in each situation whether to pull out a big gun, or if a lesser gun will work. Monsters don't have this option too much. They might get one or two Encounter (read Daily cause the monster is not coming back) powers, but once their wad is shot, they're done.
2) Healing. PCs often have quite a bit of this. Parties without Leaders aren't completely screwed (they still have #1 and #3), but parties with Leaders just wipe through encounters. Not at the start of the encounter, but part way through. Monsters rarely have healing, so once a monster is down, it typically stays down forever.
3) Action Points. PCs already have a "get out of jail card" free option. They get to focus an additional attack when needed. The vast majority of monsters do not have action points.
So if the PCs get 5 attacks in round one and the NPCs get 5 attacks in round one, the PCs are still doing 5 attacks in round six whereas the monsters are done to 1 or 2 attacks at that point.
By definition, the PCs win. This is how the game is designed to work so that PCs can be heroes that get past level 3. These are the reasons that PCs can take on an encounter 4 levels higher than the group and win. But when an encounter gets to 5 levels or 6 levels higher, it starts becoming really dicey (and even 4 levels higher is often a real challenge).
So, I opine that the rationale for adding more "get out of jail free" abilities to the game system is flawed. It's not a straight up math problem. PCs have healing and PCs have many more options than monsters, hence, they win. They don't need even more ways to win. The 4E game system is already extremely easy unless the PCs have run out of Daily resources (powers and/or healing surges).
I don't see the problem with any of this. The 4e design is deliberately meant to create a sense of urgency and danger, then allow the players to solve the problem of being behind the curve by properly employing their "dig myself out of a hole" abilities. That's what makes an interesting and fun encounter. The monsters come rocking in with their encounter powers and maybe APs, throw the party back on its left foot, and then make the players think. If the players can't effectively dig up ways to respond or they are pushed too far down the curve then they can be TPKed, but the system is pretty good about that not happening, mainly because monster's at-will attacks are generally enough below the curve that it gives the party room to work with after the DM launches his initial alpha strike.
I don't think monster healing is a generally good idea. It tends to make things tedious and works against the whole model with really very little gained. The better model is again the one that 4e actually follows, which is to give the monsters some buffs or debuffs which let the DM employ some tactics without undoing encounter progress. Truthfully once the monsters rock the PCs back the best thing is for them to die reasonably quickly once the players get back on their feet.
One way to reinject some tension in the later part of an encounter is to introduce some sort of timer. Recharge powers do this to some extent, and recharge on bloodied more explicitly. There could be some more interesting possibilities with say some monsters that could recover powers after N rounds or something like that. I'd have to say though that often this kind of thing is best incorporated into encounter design rather than monster stat blocks (and is a good reason for having wave encounters or other dynamic encounter setups).
Finally, the 'negate an attack chit' idea isn't meant to be piled on top of the 4e model. It would be useful in the "much lower hit point advancement" model, and primarily because it would effectively represent 'more hit points' without number inflation. It also breaks from the to-hit/defense divergence enough to give PCs a wider level range of opponents they can take on. It would largely REPLACE some degree of existing recovery mechanics. The model would be that the monsters would have a more steady damage output. Instead of being front loaded they would do dangerous damage all encounter. The PCs would show up, take some hits, negate them, strike back, and then start to actually be HURT. This would shift the question of when the encounter is in doubt more to the later rounds, but make the danger apparent right up front. Smart players would try to use their chits optimally but at least that would imply they take some damage right off. This could be a complex decision to make since damage no longer has to be trivial to heal.