Without any real image editing application like Photoshop, it's still useless even if it had a pressure-sensitive stylus.
Printable View
Specifically says so in the announcement specs. They may have changed it since then, but the ones reviewed on launch day did not have headphone jacks.
e: Also, that jack is noticeably larger than a headphone 1/8" jack. Might be DC power input? That or they have some seriously unnecessary padding going on.
Sensor?
It definitely looks like a hole, but when I scale the image to actual size on my display it's at least a millimeter too wide to tightly fit a 1/8" audio line, which is uncharacteristic of Apple products in itself. I dunno, I could be totally wrong on the matter, I just know that the models Engadget, Gizmodo, etc. reviewed did not have dedicated headphone ports.