The design of the PS pad has always been flawed ever since they bolted analogue sticks to it in the only place they could, to quickly compete with the N64. Sony has just been too stubborn to change the design ever since probably because, to be fair to them, the design has become iconic. I'm not sure how anyone can argue that the design of the DS3 thumbsticks and analogue triggers are "good" though, they just defy common-sense ergonomics, almost as though they got the moulds the wrong way around
These days there are much better controller designs which highlight its flaws, if the 360 didn't exist I doubt anyone would be complaining about the pads.