Okay, here is the ultimate difference, I think:
In a WRPG, you're actually playing a role as the PC. In a JRPG, you're watching the cast save the world (after directing the ATB, CTB, whatever esoteric battle system). A JRPG is like a novel with 'RPG elements,' while a WRPG is like a heavily railroaded stint of DandD.