Exactly, it all about interaction. Like the example in OneNote that I used to answer his question. I don't feel the same watching printing letters in my display than when I see my handwriting. That's something that make my notes unique. Mine. No like any other note.I can answer this one, because unlike a laptop or desktop, with a TabletPC you are interacting with device very differently, using Touch, Pen, using it in Portrait mode laying it flat on the table like a pad of paper or when reading holding it like a book. And when there is a proper Active Digitizer and it just works you just instinctively want to annotate or write down thoughts and ideas.
The way that the Pen on the SP3 works with the top button is amazing, I find my self using all the time for screen scrapes while taking notes. So when you're on a legacy form factor or even a tablet without a proper pen you miss it and continually to interact with it the way you do a TabletPC.
I was willing to compromise much of this for the form factor of the Surface 2 but as you all know I was always hunting for the elusive pen that would replicate the TabletPC and I could never find it.