But less, because of iterative attacks that drop attack bonuses significantly below expected defenses!
We can do this all day.
wow, you are really reaching now.
And actually, you would still remain wrong.
The 20s still autohit and even at -5 there is a still a large range of hit for a typical encounter. Even when you start throwing in the -10 you have reached a point where keen weapons and improved crit, etc are actually increasing the overall frequency faster than those trailing attacks are bringing it down.
No, in the approach I advocate, it is an average of 5%.
In the approach you advocate, it is an average of something probably between 2.5% and 3.5%. Yes, the rate changes from session to session. It is a random roll (or set of rolls), after all. But it averages out, as all things do.
Again, for a 19-20 threat that is a 10% threat. A typical attack has at least a 50% chance so the odds are NORTH of 5%. You are simply mathematically wrong.
Similarly, the characters they build and the threats they face have a direct influence on the corresponding number. A character with a high crit weapon and extended critical range will experience more crits, and more powerful crits. A monster with a tremendous AC might suffer a natural 20 at the hands of the party Wizard's opportunity attack, but still only take damage from a normal hit due to the Wizard's inability to reach the monster's actual AC with his bonus to attack.
Again the fact that corner cases make the 4E system a little less like the system I dislike and a little more like the system I do like is a good thing.
Their AC comes into play in every instance in 4e. It just turns out that, when you roll a 20 on the die, you usually hit their AC anyway. Offering up a critical hit on a natural 20 rewards both that random element and the ability of the character to make good on the attack. Everything you could want out of a critical hit, except maybe the not-being-a-part-of-4e bit.
You have completely changed the point here.
And the "except not-being-4E" thing is an irrelevant cheap shot and wrong to boot.
To be clear, that I dislike that system is on the list of things that cause me to dislike 4E. The fact that you are going back to the old "the reason you don't like it because you are closed minded to 4E" thing is telling.
Now, just to review. I said their AC doesn't matter because a 20 is a 20.
You replied that their AC does matter because if they only hit on a 20 then it is not a crit. I replied that this isn't significant because the math works. You have now replied that it still is significant "in every instance" and yet you concede that 20 "usually" would be a hit anyway. (For sake of argument I'll ignore that, for 4E, "usually" is more accurately "always for tactically meaningful encounters".)
We are talking about crits. For cases in which a 20 isn't required to hit a 20 is a crit. When a 20 is a crit, AC is irrelevant. So, which is it? For crits is AC significant "in every instance" or is it irrelevant in "most" cases?
There are plenty of things I want out of a critical hit system and 4E doesn't offer them.