Difficulty Scaling

[Sir_Mopalot]

So while I've run quite a few games, most of them have run between levels 1 and 10 or so. How do fighters or other mundane classes scale up in comparison to the monsters? Like, in the complete absence of magic, what stops a level 20 fight where monsters have about twice as much health as level 10 monsters from taking twice as long?

[Yuki Akuma]

Without magic, the level 20 character can't even hit the CR 20 monster half the time, and will likely end up splattered due to having terrible defenses.

The CR system is 'balanced' around the concept that everyone will have magic gear.

[Malachei]

No magic means no spellcasting? Also no magic items? Martial maneuvers are in or out?

Synergy scales disproportionately. For a classic example, look at the leap-attacking shock trooper. With the right feat choices, a high-level fighter's abilities will complement and provide synergy. An AoO-based build can gain AoO when the enemy moves, when the enemy does not move, when the enemy hits him, or when the enemy does not hit him, etc. Some of these feat choices are available only at higher levels.

Also, characters still focus fire and deal with one enemy after the other, unless they can't. If the rogue can sneak attack, at 20th level, he'll cause more than double his 10th level output due to additional attacks and special abilities.

[Sir_Mopalot]

Let me expand the OP a little. I've been working on a conversion to d20 modern to make it work as a Mass Effect game. I've been drawing a lot more about how I'm making gear work from 3.5 than d20 modern, since how gear works is a problem that a lot of people identify with it. What I'm looking for is insight into how D&D 3.5 makes the game really work from levels 1-20. While magic and spellcasting classes are probably part of this, I don't have those to work with. I do have "magic" gear to a certain extent, so there's that, I suppose. So is it mostly magic buffing and such that makes fights stay even at higher levels? Would making enemies squishier help?

(Please note that I put this here, rather than Homebrewing, because I'm more looking for insight into how 3.5 does it than anything else)