I'm doubtful, yes they sold 120,000 in 24 hours but those were to the bread and butter mac lovers. At $1500 they would still have sold a ton.
It's yet to be seen if soccer moms, teenagers, grandma and grandpa, business people, etc will all be interested. 6mil for the US is a good target, I guess it depends how fast they can roll out worldwide.
They are going to sell a lot of these things. It is pretty easy to see the hows and whys of it.
I am not sure why you think it is yet to be seen about all those people wanting it.
I was shocked when I was in line for the original iPhone and saw all those people inline with me. This device is more appealing to most of those segments you mentioned than an iPhone is.
Since there is not even a single competitor in this space, I suspect they will sell a ton. Wait until the launch comes and the 10s of millions of dollars of free advertising apple gets. Since there is not even anything else for people to compare it to, Apple is in a real good position. Much better than with the iPhone.
Some knucklehead will show Grandma their netbook and tell her why it is better and Grandma will look at them quizically knowing those are not the same things and get the iPad.
I don't know how long it will take them to sell 13 million, but they will probably have 400k-500k pre orders at least, and I suspect they will sell between 1.5 -2 million units before the end of 2010 at least.
At that point other companies will start announcing their products, and since the iPad already exists and is for sale, people who hear about those will also jump on the bandwagon.
Added with worldwide distribution as you noted, and I could see 8-10 million sold by the end of 2011.