A bus serves the purpose of a car, do you really need a car?
It just doesnt suit your needs. The millions of sales suggest tablets suit others needs.
Not sure who you know but to buy something like an iPhone new will cost you full price, its not like they will have trouble selling them.
Scenario
You are going off for a few days, taking the train/plane or whatever. You take your laptop for some films and web browsing. Unless you have a dongle, it wont have 3G to connect to the net. Unless you have a plug its going to be dead in a few hours, unless you have a specific bag you will struggle to carry it with your other luggage.
I take my 3G iPad, do some browsing, have about 10 hours of use, put it in my bag along with what ever else due to its slimness it takes up no room.
Another one
You need to check the internet for some information, maybe some news. You turn your laptop on, wait for it to boot, wait for the browser to open up then search for what you wanted.
iPad - press home, unlock, safari, search.
There are lots of other scenarios.
Do you need an iPad, no. You most likely have something that does what it does. Doesnt mean its not nice to have one though, nor will it not fill any needs.
Ask anyone that hasnt had one
''doubt i would use it, cant see the point''
Ask anyone that has one
''dont know how i lived without it''