I think Steve Jobs Refrigerator/Toaster analogy is a good one. The issue is when I use an iPad I am usually consuming information or very minimally editing. The iOS touch interface and apps are optimized for this. Consuming information minimal editing one handed operations. Even with an external keyboard this is the limitation of iOS.
On my Macbook Air, I have a full keyboard. Applications are much more detailed. More menus, more detailed operations and options. I am usually creating content. I rarely use the iPad because my MacBook Air is in my hand or lap.
To me the Refrigerator simples stores the food (iPad) but the toaster takes the food and prepares is for consumption. Everything in the refrigerator is for storage no preparation. The "cooking" is done on specialized devices and by the cooks once withdrawn from the refrigerator (my MacBook Air)
Just my 2 cents
I'd agree with the above as far as the current Apple device offerings are concerned. But wouldn't there be some value in have a single device that could realistically do both jobs by allowing the screen to function as tablet when separated from the keyboard?
Admittedly it would be a larger tablet than an iPad - I think 12" is the sweet spot for these kind of 2-in-1 devices - but one could imagine a Broadwell Core i3 or i5 as being suitable for a 12-inch iPad running some touch-enabled variant of Mac OS X, as well as being a fully featured laptop when connected to its keyboard (containing the ports, SD card etc.)
I'd personally welcome a 12 inch tablet, if it were light enough. If this were combined with a MBA style keyboard (containing additional storage, battery, ports etc), this would be compelling. It could even offer a dual iOS/Mac OS X operating system and both ARM & Intel CPUs, provided they were sufficiently low powered).
This is nothing new - there are Android tablets doing this already. It remains to be seen whether this form-factor is really what catches on, but I do see general purpose laptops getting smaller and lighter, and once everyone already has 7-10" tablet, manufacturers will be looking to provide some value-add in the form of hybrid laptops.