Ahem, you have not owned every tablet PC, becuase if you did you would know about Gateway's (now discontinued and sadly not replaced) C-140X. I own one of these tablets, and two years after purchase, after much use, the batteries last almost exactly half as long as they used to, 6 hours. With new batteries, it will run 12 hours no problem. I'm typing this reply on it right now. Yes, it is a bit large (14 inches) and heavy (haven't weighed it, but probably close to 8lbs with batteries) but I've taken notes on it for the past two and a half years, and it has been fantastic.
That being said, I think you are looking for something closer to what Lenovo has released with their C2D/snapdragon powered thing. I'm really, really glad Lenovo hasn't turned into another Laptop mill.