I have experienced this only after very long sessions of Forza 2, where my finger would start to hurt from the pressure(resistance) . I think its just down to each persons hands so no real answer i guess...
How tiny are you? Are you like a kid or something?
Im 192 cm tall, about 90 kg, small sized hands for my body size, and my hands slip all of the time of the DS3 controller.
The design is just broken, trigger should curve the other direction in order to ensure maximum grip. In my hands the DS3 controller is a pain to use in Grand Turismo if you use the triggers as accelerate\brake. My hands keep on slippery, or they start to hurt because they have to really hold the controller with alot of force not to slip. (i just use R\L 1 instead ..)
I do agree thought that as a button its nicer to use, its shaped rounder so its more comfy for the fingers when you push the button down.