Well.. if you didn't already figure this one out yourself, here is a list from the top of my head:
With a laptop:
1) You can't hold a laptop with the lid open in one hand and use it (for a long period)
2) You can't remove the keyboard from the screen if all you want to do is read/watch movies (it's stuck there forever)
3) You can't use the screen to navigate (you need the touchpad or "joyknob" or mouse)
4) You don't have a camera on the back to snap pictures
5) You usually have to carry an extra bag/backpack (charger, cables, mouse, ..)
With a tablet:
1) You can't read/write DVD's
2) You can't use it for high CPU/memory intensive tasks (coding, video editing, 3D raytracing,etc.)
Most people can perfectly combine a tablet and a laptop for their tasks: a laptop for coding/video-editing/burning, and a tablet for email, ebooks, twitter/fb, movies, music, (video)chatting, pictures and browsing.
rom: Stock JB
spl: ? | radio: ?
rcv: CWM Recovery
(backup: Nexus S, HTC Magic 32A)
(tablet: XOOM, Nexus7)