If you spend any time at all with an iPhone or iPod touch, you’ll be happy with their power and their portability, but you also will see the need for a 10-inch version, for times when a larger screen outweighs the need for pocket transport, but you still want that same simplicity and ease of use and less than a kilo weight.

A 10-inch display can show a Web page, a DVD-quality video, a photograph, or a page from an eBook or PDF, all at what is essentially full-size. It can run full-size apps like a spreadsheet. If it has touch, it can replace all kinds of paper, you can hand it to people to sign a PDF or tap an “agree” button and you won’t have to explain how to use the device because it’s “see button, push button”.

Imagine a writer in the 1950′s with a typewriter and paper, a stack of reference books, and a tiny pocket notebook. The notebook computer replaces the typewriter and paper, a 10-inch tablet replaces the stack of reference books, and an iPhone replaces the pocket notebook.

So we are already paying out our tablet PC money, but we’ve been getting back stacks of reference books. Now, the cost of paper and ink is so high that print publishers could subsidize a big iPod in the same way AT&T subsidizes the iPhone and still come out ahead. The only argument against a 10-inch tablet is the stack of books. It’s one or the other. Note that the tablet PC is becoming the cheaper option fast.

Another way to look at it is that the print medium is going to switch from ink on paper to HTML5/PDF on tablets.