Also, the external keyboard is only for when you want to use it like a laptop, doesn't mean it's a permanent set up because it's not always necessarily convenient. I agree with Greenlig it's better where it can fit better into your lifestyle because it has better portability and its interface (with help from touch) makes accessing applications and data more ergonomic and of course, easier. For some it might not be worth the price tag, for example, I am happy with my laptop...though I could one day be tempted to get tablet if I have the money to dispose of.
I think tablets can be better suited for some people, for example, I think a tablet would be of more use to my mum than a laptop.
Of course, you could also make the best of both worlds and get a hybrid of the two, for example, the
ThinkPad Twist, it's a convertible ultrabook, but it's a lot more expensive than any regular tablets.