Hello Netnovice.

There will always be consumption devices vs developer devices.
More precisly, End-User devices.

The end-user devices such as Tablets and Droids have opened computing power down to the most common end user.
Access to information from anywhere. This does not limit the desktop, this expands the desktop since there has to be someone to develop the applications for the consumption devices and this is done on the desktop. To support the end-user devices from development to customer service, desktops are required.
I work in the mainframe environment. I remember when I started everyone said mainframe was a deadend career path. That was in 1994. BTW I hate mainframe, but it pays the bills.

After you have been around for 10 - 20yrs in the compute industry you can summarize the theory down to:
Every new platform is going to wipe out the legacy or previous platform. Chuckle and walk away from that line of resoning.
Last but not least; there are 7 Layers of the compute platform. The application layer is the last layer, the closest to the user, and supported by 6 other layers. You are arguing 1 - 7th of the model.

[post edit]

I've started to read through this thread. Don't believe marketing and saleperson hype.

Tablets aren't even marketed as PC substitutes. They're all intended to supplement a computer running a general purpose OS, although that computer could well be a netbook.