I didn't say it was an either/or proposition, I said that touchscreens simply have no advantage over the mouse in a desktop environment at all. They cost more and don't offer any improvement, and are therefore useless in that context, whether you use them in addition to a mouse or not.
Touchscreen's don't really seem to be suited to the desktop... But then I'm not sure the desktop has long left for this world... I use a laptop at work (though it is chained to the desk), and only have laptops at home now... The tablet, or rather the iPad (since no other tablet computer has really taken off yet), has encroached on much of the traditional Laptop space, while the laptop has taken most of the desktop space (though there will always been a need for more powerful machines that can't exist in laptop form).
It would be crazy to think that newer smaller forms of computing won't eventually replace the larger older units... Look at what happened to Mainframes, then Minicomputers, etc...
