I was wondering if anyone else noticed this?
I have a PX-120 too. When comparing the 120 to the 130,
the 130 headphone output is much lower through the same set of headphones. With the 130, I have to have the volume up on full to get any level out of the phones output.

I have a px330 which should be the same as the 130 since they both have 8w per channel and the headphones do not seem low volune to me at all. i can't really even turn it up to the halfway point without it being too loud. It would be good if you could compare another 130 at the store to see if your's has a defect in this regard. Maybe though call casio customer service or if you have 30/45 days to do an exchange (provided the problem is with just yours and not all 130s!) go that route.

I was at the Guitar Center Saturday checking out the PX130. With my phones, I had the volume set below half. More than that, and it was getting pretty loud.

Wolfetho
You might want to check the impediance of the headphones you are using. Some headphones take a lot of wattage to drive the drivers. If you have or can borrow another pair, try those. If it still does the same thing, there is something wrong with the headphone jack on the piano. I remember when I played a PX-130, the sound was loud through the earbuds I was using and I thought the sound was distorting from all the volume.

Yes, generally the headphone output volume of the Casios seems to be quite hefty compared to Yamahas. The behavior described by the OP sounds far more Yamaha-esque than Casio...

Thanks everyone for your replies.
Yes, I tried a different set of headphones (Grado), and they were much louder.
It must be the impedance of the AKG 240 headphones.
Not only were they much softer, but they were also not as clean
as the Grado's. Big difference!