“If the appropriate action is obvious to the user, the time actually required for that user to tap the proper spot on the screen is miniscule. Confusion about where to tap wastes far more time than an extra tap.”
I noticed this while introducing my parents to the iPad. They figured out how to interact with it — touch — within seconds. That’s because touching with the fingers is an innate ability. With that down, they could “forget” about how to use it and just start using.
Conversely, watch a new user hold a mouse for the first time; he’s got to learn how to get it perform the actions he wants to do on screen before he can progress to running software. It’s like preparing a new dish for dinner, but the recipe is in Chinese.
Touch completely removes step 1 and lets the user get right to interacting with the software. As “a better mouse,” the Magic Touchpad introduces that ease to the desktop.