Here's a kind of backwards way of looking at it.
I'm no physicist, but isn't there a basic principle that speed*mass=force or something like that? To put it another way, a sling stone tossed at you underhand is going to hurt a lot less than one moving at you at 100 MPH: the faster it moves, the more damage it does.
Same thing with a fist. Someone who nudges you with a fist isn't going to hurt you nearly as badly as someone who strikes you with incredible speed with their fist. Faster the fist moves, more it hurts.
Got it? Move fast = hurt more.
Now, let's work backwards. High strength = hurt more, right? A significant part of why is that you're overcoming the inertia of your weapon to a greater degree: you get it moving faster, so that it hurts worse.
High strength=hurt more
Move fast=hurt more
High strength=move fast.
That might seem counterintuitive: you'd think that dex is what makes you move fast. I'd say that in battle, though, dex gives you precise movements; strength is what lets you get that axe or fist moving quickly.
With me so far? There's one more step.
When you're trying to hit someone, you can do it in a few ways: you can strike precisely for their unguarded areas, or you can attack so quickly that you either hit before they get their defenses up, or you can hit with such force that you bypass their defenses.
Striking precisely is the purview of weapon finesse. Striking with great speed is, as we've seen before, a function of strength. Breaking through defenses is also a function of speed.
And when you make a touch attack, normally you're trying to strike with such speed that they can't dodge out of the way. That's a strength function. If they have a deflection AC bonus, you also want to bypass that: that's also a function of strength.
Ergo: to make a touch attack connect, you want to be strong.
Told you it was all backwards.
Daniel