Why can't we have an ipad which can truly replace a laptop ..
Give it time. The iPad is still in it's infancy. With each update, it will be able to do more and more. Heck, the next update to the macbook pro line is rumored to be getting rid of the optical drive, and the macbook airs already have. The line between the laptop and tablet are beginning to blur.
Personally i love surfing the web on the iPad much more than on a laptop. And the touch/finger swipe is becoming so ingrained in our collective tech psychology that Apple is incorporating it into Lion and shipping imacs with touch pads. So many programs lend themselves to the intuitive nature of the touch pad/screen.
In time, iPads will become powerful enough to do many more things that the laptops currently do. The line will continue to blur. But it will take time.
For power users, the laptop is still going to get the nod.
But some are already making the transition. I travel alot, and always bring my ipad instead of my laptop on the road. For one thing, i prefer it for surfing the web and writing emails and updating my blog. I also like it for loading and looking at my pictures i take with my dslr. I don't have an ipad 2, so editing videos in imovie is not possible on my ipad 1(dont want to jailbreak it)...so i do without some features.
When i update to the iPad 3, i will be able to edit video, and won't miss my laptop at all when on the road.
When i get home from a trip, i do most of my heavy editing on an imac....but more and more, i see the iPad becoming my only tool for when i travel. Even at home, i prefer to watch movies and surf the web on an ipad over a laptop.