Let's analyze the scaling behavior of the average number of hits to kill a monster in 4E D&D itself, with some very egregious extrapolations.

Recall that the average number of hits to kill a monster (N) is the ratio:

N = (monster hit points)/(average amount of damage per successful attack).

From the 4E PHB1, the damage done by at-will powers is typically:

[W] + stat mod + magic enhancement.

Stat increases happen at levels 4 and 8, where +1 is added to two stats of choice. We assume one of the stats goes into the primary stat.

At the paragon and epic tiers, the stat mod increases happen at levels 11, 14, 18 (paragon) and levels 21, 24, 28 (epic). At levels 14, 18, 24, 28, the stat mod increases are similar to the ones at levels 4 and 8. At levels 11 and 21, the stat mod increases are +1 to every stat. (This is on page 29 of the 4E PHB1).

The magic enhancement for different levels assumes the table from page 225 of 4E PHB1.

1 -5 -> +1

6 - 10 -> +2

11 - 15 -> +3

16 - 20 -> +4

21 - 25 -> +5

26 - 30 -> +6

(ie. Magic enhancement increases by +1 every five levels).

To make things simple, we will examine the levels 11-30 of paragon and epic tiers as one entity. Over levels 11-30, the total additional damage contributed by the stat increases and magic enhancement is +7, due to +3 from stat increases and +4 from magic enhancement, by the time one reaches level 30. (Heroic tier by level 10, typically already has a +6 to +8 contributed to the damage, where: +3 to +5 is from the stat mod, +1 from the two stat increases, and +2 from magic enhancement).

One egregious assumption we will make, is that this pattern of stat increases and magic enhancement remains the same every 20 levels as one goes to higher levels beyond level 30. For example, stat increases at levels 31, 34, 38, 41, 44, 48, etc ... and magic enhancement increases of +1 every five levels. In effect at level 50, the total additional damage contributed by stat increases and magic enhancement is +7.

So above level 10, the increase to damage from stat increases and magic enhancement scales approximately as: 7*(level-10)/20

Another egregious assumption we will make, is that the damage of at-will powers [W] increases each ten levels after level 10, in the pattern of:

level 21-30 --> 2[W]

level 31-40 --> 3[W]

level 41-50 --> 4[W]

level 51-60 --> 5[W]

etc ...

So above level 10, the average damage from a successful hit scales approximately as:

level*(average[W])/10 + 7*(level-10)/20

(We will ignore the heroic tier stuff, since it will just drop out as a constant when things scale with level. But for reference, the heroic tier will contribute a +6 to +8 to the damage by the time one reaches level 10).

On the monster side, the hit points of various monsters from page 184 of the 4E DMG1 are:

ROLE*(level +1) + CON

where ROLE is:

Artillery, Lurker --> ROLE = 6

Skirmisher, Soldier, Controller --> ROLE = 8

Brute --> ROLE = 10

(Elites double the hit points, while Solos quadruple the hit points).

Now the average number of hits to kill a monster being attacked by a player (of the same level as the monster) is approximately the ratio (for a high level):

N = [ROLE*(level+1) + CON]/[level*(average[W])/10 + 7*(level-10)/20]

Taking the level to infinity, this ratio approaches the limit of

N -> ROLE/[(average[W])/10 + 7/20].

(If one actually ignores the egregious assumption of weapon damage [W] increasing every ten levels, then the average number of hits to kill a monster is just:

N -> ROLE*20/7

as the level increases to infinity. In this scenario, the at-will power [W] remains the same for all levels. At level 21, [W] remains [W] and does not increase to 2[W]).

Let's plug in some numbers. For a skirmisher monster, ROLE = 8. For a weapon with d8 damage dice, average[W] = 4.5. For these numbers, the average number of successful hits to kill a skirmisher being attacked by a [W] = d8 weapon is N = 10.

For different [W] weapons attacking this skirmisher monster, we have average number of attacks N as the level goes to infinity:

average[d12] = 6.5 --> N = 8

average[d10] = 5.5 --> N = 8.89

average[d8] = 4.5 --> N = 10

average[d6] = 3.5 --> N = 11.43

average[d4] = 2.5 --> N = 13.33

More generally for different monster types with ROLE:

Artillery, Lurker --> ROLE = 6

Skirmisher, Soldier, Controller --> ROLE = 8

Brute --> ROLE = 10

(Elites double the hit points, while Solos quadruple the hit points).

For various weapons [W] dice, this limit is:

average[d12] = 6.5 --> N = ROLE

average[d10] = 5.5 --> N = ROLE/0.9 = 1.11*ROLE

average[d8] = 4.5 --> N = ROLE/0.8 = 1.25*ROLE

average[d6] = 3.5 --> N = ROLE/0.7 = 1.43*ROLE

average[d4] = 2.5 --> N = ROLE/0.6 = 1.67*ROLE

average[d2] = 1.5 --> N = ROLE/0.5 = 2*ROLE

(d2 is flipping a coin, where one side is 2 and the other side is 1).

Indeed with these egregious extrapolations, 4E D&D is "always fighting orcs" as the levels go to infinity.