They probably rushed it to get it out in time for some fighting tournaments. You're right about graphics looking great though. As for the story, well...I don't think Tekken was every really known for their story telling. Kind of a shame they didn't put much thought into their new characters.
The graphics are great and as ever they have some cool characters but none of them have much info like who's Lucky Chloe? Who's Claudio? ffff just blanks... It clears up the mishima story though if you want to see about the family and why there's so much fighting between them. That's about it... and its short. Not to mention CPU is hard as shit on the last few chapters