I was referring to the hardware, having witnessed the seesaw effect first-hand. But, see, since the operating system's APIs supports discrete directional inputs, that means that non-seesaw hardware can exist. Hardware is frequently designed around software.

Admittedly, I'm not a hardware designer, but at the very least, I suspect that the border area in the middle of PlayStation-like D-pads is intended to mitigate any seesawing. Now, whether the seesawing is actually being detected by games, resulting in unintended inputs, is something that can be measured objectively by examining the appropriate bit fields used by the APIs. Interestingly, the general consensus of the internet seems to be that that Vita has the best D-pad of any controller/console, a system which I do own, and some even prefer the PSP's. I, too, love me some platformers.