Partly, PC dominates here because the game released about 18 months earlier here on PC than PS2, and partly because SCEA only made and sold the hardware required to run the game for about 9 months (March 2004 - November 2004). In Japan the game launched on PS2 6 months before PC, and the hardware was much more widely available and for a much longer time span (2001-2009 or 2010). There simply aren't as many HDD units in North America, so there's a smaller player base because SCEA created that scarcity.

Meant to edit this into the previous post, whoops.