[darkstormvx]

I believe the tendency of the boxster is to oversteer and possibly the manufacturer recommended the psi to offer more control in a high speed cornering situation, as well as during daily driving, where turn-in is more valued at low speeds.

Higher pressure promotes more high speed stability, however the tire takes a while longer to warm up. Slightly less grip. Slightly lower tire footprint.
Lower pressure gives you more flexibility and better cornering as the tire warms up more quickly. Larger tire footprint. More grip. Yet wears out more quickly as well.

I assume making the rear more stable and the fronts more nimble and grippy makes the car a better daily driver and helps the tires wear more evenly. I have 19" wheels and follow the manufacturers specs and love the handling.

I'm not sure what you're feeling, but I know if I need to slow down or brake quickly I want to more turn-in ability from that oversteer and grip in the front. Everyone drives differently tho. And you may prefer a different setup. The best setup is the one that works for you that you can feel. The manufacturer has to cater to the needs of the normal daily driver.