I see that hybrids seem to encompass many many different bikes and some of them seem to pushing the limits of what I would consider a true hybrid. What in your opinion is a hybrid and what should it be able to do.
For me, a hybrid should be able to be a decently fast road bike or a moderately tough mountain bike for unpaved roads or trails. It should have mounts for fenders and racks to make it a commuter.
I have an 07 Specialized Sirrus and it fits what I consider a true hybrid. With 23mm road tires, it is fast and easy to pedal. With 32mm off road tires, it can function as a mountain bike for reasonable trails. Right now it has 28mm city tires, reflectors, headlight, fenders and rear rack and it my commuter/exercise/dog bike.
With a simple switch of the tires and a few accessories, it seems to be able to fills many roles quite well. It is a jack of all trades.
By contrast, I don't consider a mountain bike with slicks to be a true hybrid because they don't make good road bikes when needed. It seems the Sirrus and Treks got it right with the geometry and frame. Not quite a road bike but not a mountain bike either. They are something in the middle and that is the point.