The iPad and the Macbook Air need to basically become the same product.
Kind of like the tablet laptops Toshiba was shipping about 7 years ago. You open the laptop and it's a Macbook with touchscreen display and keyboard. You swivel the screen flat onto the keyboard and it's an iPad. Maybe some apps work in only one mode or the other, but your files will be available to both kinds of apps, X and iOS.
Perhaps, but nobody wants to carry around (and charge, and sync) two devices when they could carry around just one.
If I had a device that worked like a MacBook and an iPad, so I could use it like a laptop at a cafe and like a pad on the train, that would be a pretty damn neat device to have. And eventually, I probably will.
Something like this: http://aidacase.com/keycase-folio-deluxe-with-built-in-keybo... might work for you eventually, though it may seem silly. I think the difference in this is that you can just open the front flap for quick, instant-on tablet access, and unfold it further for keyboard usage vs. having to set up / maintain two different systems or use a tilt/swivel joint to access the touchscreen.
I could really see them converging in the not too distant future when Lion is released, bringing more touch friendly concepts like the Launchpad to OS X.
Kind of like the tablet laptops Toshiba was shipping about 7 years ago. You open the laptop and it's a Macbook with touchscreen display and keyboard. You swivel the screen flat onto the keyboard and it's an iPad. Maybe some apps work in only one mode or the other, but your files will be available to both kinds of apps, X and iOS.