The problem is, there are lots of PS3 supporters that are under the notion that JRPG's would sell much better on their console (due to all the JRPG fans from the PS2 moving up) as opposed to the 360. This has yet to be proven, so when games like Valkyria Chronicles or Eternal Sonata do poorly, it's the reason people like mrstickball come in here and flaunt that fact.
I think things point to the 360 userbase having a bigger JRPG userbase in the west. The PS3 offsets this with their advantage in Japan, so it comes out almost equal (slightly PS3 favored). The Wii should prove to have the most, but that's a different matter.
That would explain why it is so hard to tell which system has more JRPG fans.