It lets those who enjoy reading have immediate and portable in-hand access to their favorite reading and reference materials. The computer does not.
When I read extended texts, I like to concentrate for long periods on that text. If I leave off somewhere, I like to be able to find my place quickly and easily. The Kindle is a dedicated device that builds in the functionality to do this. The computer does not.
Would I subscribe to the New York Times on the Kindle? Sure, if I have lots of money and value the convenience more than the expense. It is nice to be able to switch instantly to the news while reading your book on a commute train. But, not really if I don't want to spend where I don't have to spend. Not when I can get access to such news sources over the web.
Don't see that the issue of multi-tasking versus uni-tasking has anything really to do with this.
News publishers who want to sell paid content will benefit incidentally from any superior reading platform that will induce some minority of the reading audience to pay for their subscription just to have all their reading material in one convenient place.
But uni-tasking is not a deus ex machina for the news business.
If I put pure uni-tasking as my primary reading aim, I will sit back in the comfort of my home, pull one of the wall-full of antiquarian books I own off the shelf, and through myself into it without distraction.
If I am riding a commute train, or flying on a jet, I will take the convenience of a superior reader, uni-tasking or not, and I will probably like it all the more if it lets me do many things at once as I travel.
If your users spend 90% of their time using two features, maybe it's because you've made the other features suck.
While I am now an Apple fan, this reminds me of the ridiculous excuses Apple fanboys gave me when they compared their early-generation iPods to my MP3 player at the time (a Rio Karma).
"It doesn't support gapless playback because in modern times, you should focus songs not albums!"
"It only holds 10 gigs, because you should only listen to your best songs on the go!"
"You don't need a button for skipping tracks, because you should spend your time listening to music, not switching between songs!"Uh, when I read that passage it was the only thing I was doing. I often multitask, but not all the time or even the majority of the time. And as others mentioned, it's not like the Kindle encourages "unitasking" any more than reading a book does.