I do not disagree, engineers need CAD tools or simulators, architects the same. Take all the professional people and put them in the category "Need a computer for their job." Now create another group called "Don't need a computer for their job." Compare the sizes of the two groups.

I don't think anyone expects that general purpose personal computers are ever going away, but there is a pretty compelling argument that the bulk of computational assets will fall into the 'appliance' category rather than the 'general purpose' category.

As Atwood points out, Microsoft strove to have a PC in every house, and they succeeded! PCs have higher penetration in homes than TVs. However, given tablets and their capabilities, it is looking more and more likely that this trend will stop and that the number of homes without a PC in them will begin to rise again. its an open question how many homes that will be but it seems likely it will happen.