The pc will remain the main gaming system for me, all I am looking at is whether there are enough rpg's that are exclusive to the xbox for it to be worth it for me to own both an xbox 360 and a gaming pc.
Seems so far I should stick to the pc only option.
Hmmm... well I guess I'm also allowed to pitch in my 2c

Well with all the different types of RPG's available (Story, Strategy, Action, Hack 'n Slash, FPS, Turn-based, JRPG, etc...(some of them are similar)..it's quite tricky. Their maybe more story driven RPG's on PC but before you cancel out the Xbox let me tell you my story.
I've been a RPG fan all these years...from Diablo to Dungeon Siege to Fallout 3 and even Final Fantasy 1. I never liked any RPG except action or hack 'n slash loot fest ones...but after I gave the turn based / JRPG, etc a try I was really amazed at how much I enjoyed them. Yes some RPG's maybe story locked but you still create the character YOU want and play the way YOU want, learn the skills YOU want, etc. In the end RPG's are fun because you play how YOU

want to.
I'm not saying go for the xbox or other console but before you write the box idea off...please just look at the other RPG's available and maybe you might even be surprised by the results. Also keep in mind that since you only play single player RPG's theirs no need to go for anything higher than the R1799 xbox arcade...and hey you can still enjoy non-RPG xbox exclusives aswell
To make life a little easier I have compiled a little list to give you some indication
Note: Some of the following titles will also be available on PC but I listed them aswell incase you never played them before.
The Last Remnant (new FF based RPG)
Fallout 3 (also on PC)
Fable II (on PC ..no ETA)
Infinite Undiscovery (similar to the FF series)
Tales of Vesperia (fun if you like the Tales based games)
Lost Odyssey (great if you're fan of Final Fantasy)
Kingdom Under Fire: Circle of Doom
Mass Effect (also on PC)
Eternal Sonata (stunning)
Two Worlds
Blue Dragon
Phantasy Star Universe (pretty good)
Marvel: Ultimate Alliance (oldish but fun)
Enchanted Arms
The Elder Scrolls IV: Oblivion (lots of multiple paths - also on PC
Upcoming RPG on Xbox
Rise of the Argonauts
Alpha Protocol
Borderlands
Dungeon Hero
Marvel: Ultimate Alliance 2 Fusion
Age of Conan: Hyborian Adventures
Arcania: A Gothic Tale
Elveon
Sacred 2: Fallen Angel
Star Ocean: The Last Hope
Divinity 2 - Ego Draconis
Two Worlds: The Temptation
Blue Dragon 2
Dragon Age: Origins
Final Fantasy XIII
Mass Effect 2 & 3
X Quest
Defense Grid: The Awakening
Hope this helps.