I never really GOT the JRPG/WRPG split. I tend to blame the popularity of Final Fantasy in America, though, because... well, here.
The Dragon Quest games have ALWAYS been fairly Western in their sensibilities, even if they're also regarded as some of the most Japanese of the JRPGs. But storywise, they're very European classicist. From a gameplay standpoint, things like classes and the level of controlled open-ended-ness that the DQ games have is also very western, and the DQ battle system has a much more traceable lineage back to Wizardry.
Same with Phantasy Star. Wizardry-style battles, first person dungeons, and a degree of non-linearity and adventure gaming aspects.
Actually, you know, the first three FFs...
So let's say it was FFIV that caused the split.
And the notion of reducing a story's importance in a WRPG is... I actually have no idea where that came from. I blame Bethesda. Originally it was because of text limitations, like with the console counterparts, but later Ultima games were always story heavy, and Black Isle's games are DAMN story heavy, and there's also stuff like Krondor.
So in a sense it's hard for me to say what's distinctly Western about WRPGs. In general I guess they tend to be a bit more staid -- you're not going to see something really outlandish come out of them *generally*, whether it be a really bizarre battle system or character growth system, or just a particular visual style, like how early PSX Square RPGs were pretty dadgummed... well, you know how FFVII's pre-rendered backdrops were. Slightly wacky.
At the same time I wouldn't say WRPGs tend towards realism, although Oblivion kind of did (And that's one of the reasons I liked Morrowind better. More rich chocolate GIANT MUSHROOMS please!)
You also don't get a lot of action RPGs in the West, and when you do, the action elements are way more FPS than the uh... they're not so Zelda-ish. Partially I think this is hardware related, a little. During the DOS era, games tended to run kind of choppy which is suckish for an action RPG, and console controllers are a bit rubbishy for FPSes.
Summatively, battle systems in WRPGs tend to be a bit more integrated and seen more like interfaces to a particular set of gameplay mechanics whereas in JRPGs they're more like minigames, sometimes.
Maybe the biggest difference is aesthetics.
(Summary of deleted intro: MagiNation would've been funner if it hadn't been so damned slow; is Black Sigil trying too hard to be japanese or trying too hard to be oldschool?)
The one thing that Western developers have not been able to get right is the turn based battle system.
Well, if you cherry pick three games out of a 20-year history of games, you can pretty much back up any statement you want to make. Septerra's battles, in particular, are noted as being usually slow even by WRPG aficionados, and Sonic Chronicles is, uh, irrelevant.
Admittedly, there HAVE been a lot of slow turn based battle systems in recent WRPG history -- Wizardry 8, for instance, although partially just because of how LARGE the battles could get, and even some old games like GoldBox were notably slower than other tactically-based WRPGs like Ultima 4-6 -- but, like, Might and Magic 3-5 (And 6 and 7 too if you view them relative to the fact that battles usually involved upwards 30-50 enemies), The Bard's Tale and its lot, Wizardry games prior to 8, Albion, and the entirety of the roguelike subgenre... Even the Fallout games, though they can have lengthy battles, aren't prone to a lot of down time like Septerra was.