parallel port is not the same. It doesn't support wide range of voltages, internal pull-ups, or the ability to assign functions to the pins. I guess assigning functions makes them SPIOs (special purpose, rather than general purpose). But having the hardware be able to generate an interrupt for any pin, or use hardware fifos for I2C and SPI is a huge advantage.
The ASRock D1800B-ITX is a neat board, but getting the ATX power supply is going to cost more than a Raspberry Pi. I suspect you'd end up spending around $180 getting the board, psu, ram and ssd. Still not a bad deal, but not really in the same category as RPi for price.
A better comparison against an ASRock is the Nvidia Jetson TK1 dev kit (newegg carries them) is $200. And include quad core ARM, GPU, 16GB flash, 2GB RAM and power supply. It's a bit smaller than an ITX board, and quite a bit larger than a RPi.