As someone who read at least 2/3 of the DOS 6 manual when it came out, and have used a variety of Linux flavors as well, a command prompt is the least helpful interface devised. What do you type there? How do you let the computer know when you're done typing? If the answers seem obvious to you, think about why, and what on the screen would point you that way if you hadn't had training. People are very visual, in general, and a simple interface such as a mouse that directs focus and has a minimal amount of interaction options is far easier to get started with, especially if the GUI has culturally intuitive icons (save needs updating).

I don't think the power of the command line, or text interfaces in general, can be overstated, but even the most helpful text interfaces, such as those found in some IDEs, require prior knowledge to be useful. This isn't going to work for the majority of people.