I haven't played IL-2 and AH enough to note this similarity in the edge of the flight envelope he discusses.
But, having said that, I don't find that the IL-2 planes fly 'the same' THROUGHOUT the flight envelope. I do find them different. I don't find the differences as noticable as in AH2.
I've been trying to quantify my feelings with respect to the FM of IL-2 vs. AH2, and I just don't know where I come out, having never flown a WW2 plane.
Sometimes I feel that the IL-2 FM is 'hard' just for the sake of being hard. Like someone else mentioned, I find it incredibly difficult to get a stable gun solution on an even non-maneuvering target. No plane should be that unstable. And, in IL-2, I find it much harder to 'hit' the target.
But, I also find the damage model in IL-2 more 'believable', the missing stab issue notwithstanding. I have milked a few planes home full of holes, and the FM definately changed in response to the damage. Furthermore, I've had killshots on enemy planes where I didn't know for sure if the plane was dead, or just evading low.
In AH2, I find it much easier to get a gun solution, even on a maneuvering target. The damage model, while certainly acceptable, is very...similar? for each plane. I shoot the plane and the flap comes off, or an aileron, or the engine oil, or the fuel leak...it's the same sort of damage to every plane, and I've become accustomed to being able to tell how much damage I've done to an enemy plane. I usually know right away if I've done fatal damage to an enemy in AH2; in IL-2 it's much harder to tell.
At first I was thinking that IL-2 had the more 'realistic' damage modeling. I didn't thing many pilots were landing 4-5+ kills in a sortie in real life, and in AH2, with good ammo management, you can rack up tons of kills in a single ammo loadout. I've rarely killed more than 2 planes in a sortie in IL-2- it take too long to get kill damage with a single ammo loadout. But then I've been watching Dogfights on TV, and it sure seems like there were plenty of 4 kill sorties in Pony's and other .50 cal birds. So maybe AH2 isn't so wrong after all....
Overall, I find that both games bring something different to the table. You can't go dropping bombs on ships in the Coral Sea from your Betty in AH2, and you can't go to CAS in your Beaufighter in AH2. You can't fly through a thunderstorm, or fly on instruments.
In IL-2 you can't get even remotely the same kind of coordination you get from a real-life human wingman in AH2.
I have both, play both, and am happy to have the choice on any given day. We've really come a long way in our simming these days.