Example would be games consoles and the amazon kindle, in fact plenty of people will have 2 games consoles to play different kinds of games (e.g wii and xbox).
I think the main draw of hybrid devices is where buying individual devices is unaffordable to most people (e.g cars) whereas the price is computing devices seems to be coming down.
Dedicated devices have other advantages too, for example if your kids are bored you can hand them your tablet or let them play xbox while leaving your laptop free to work on.
it might also be nice to have a hybrid device if carrying two devices is cumbersome. However in the event that you will be carrying a laptop, you probably have it in a bag find that a small tablet will fit comfortably in there also.