PS2 Analogue Revealed!
Well, it took me a minute but I figured it out. The buttons for the PS2 are really well designed, IMO. Unlike the Namco NeGCon with it's little POTs on every button, the PS2 uses a much simpler and cheaper design. If you've ever opened up a game controller, and I'm sure most of you regular visitors have, you've seen the same thing time and time again: little black pads under your buttons that connect two gold or silver pads on the PCB inside, completing a circuit. The PS2 is completely different - the first thing you'll notice inside is that the 'PCB' has a single solid line across where the two halves of a normal PCB button would be.
Until I get pics (And I apologize for a lack of, Future Shop is taking forever to get my camera back!) I'll skip the rest and jump to the theory. The bottom of the black pads are rounded like the bottom of a sphere, instead of flat like most controllers. As the button is pressed farther and farther down, more and more of the button comes into contact with the 'strip' on the PCB. The resistance of the button is lower than that of the strip, so this results in more and more voltage being passed through to the controlling chip.
[PS2 Button Diagram]
Pardon my amazing lack of art skills.
You want to redo it? Fine, then shaddup.

You may or may not be able to see here how the pad comes down to the strip, and as it makes more contact the signal passes through the lower-resistance pad instead of the strip - signalling the button's differing pressure.
I do have a fear, but I'm sure that Sony's thought it out and my fears are groundless (hahahahaha!). If you get better results from pressing harder on your buttons, aren't they going to wear out too damned fast? I mean, chances are any heavy gameplay has worn out your current sony pads already! Get ready to shell out for new controllers a whole lot more often. =/

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