I think the comparison between an iPad and mini-laptop isn't helpful.
The iPad is an instant on device not meant for type intensive data entry. Also, like the original Palm, it should have quick, resource light, applications that launch quickly.
A laptop is overkill for the situations where a tablet form factor is preferable. In fact, it can be argued that many laptop users didn't buy their laptops to take advantage of all the power laptops offer. Instead, they bough them because they are only viable mobile devices with a reasonable amount of power to perform the tasks they want.
Additionally, laptops, while mobile, are generally hampered- They need to be placed on a surface, either a table or a lap, to be able to type effectively. This is also necessary to launch programs which also must be navigated from a position where the trackpad is usable.
A tablet, on the other hand, is ideal for a number of mobile situations that laptops are currently used in for lack of a compelling alternative.
And I wouldn't put a desktop OS on a tablet either. Microsoft has proven the difficulty in this and for Apple it would only dilute OS X and diminish the experience of using, particularly when compromises are made to the desktop OS in order to accommodate the touch interface.