Currently, DC Comics are available on the iPad, the iTouch and other readers that allow apps like Comixology which works through iTunes.
Presently, the Nook, which has been kicking the stuffing out of the Kindle with it's color version has been slow to grow it's library of graphic novels or comics and many have complained that it's selection of Magazines has been growing at much to slow a rate.
Barnes and Noble didn't take kindly to the DC Comics deal with Amazon, and in a move that some are calling a tantrum, they pulled those same 100 graphic novels out of their stores.
It seems short sighted on both companies parts. For B&N they should have kept in mind that exclusive doesn't mean forever, look at the iPhone which initially was offered only through AT&T and now works just as well with Verizon.
DC hasn't seemed in a great hurry to make their books available to the Nook either. In fact no publisher has, due mostly to an increasing fear of angering their base of comic book shops who offer their primary means of print distribution.
Still, at a recent lecture before a hundred high school aged comics fans there was no hesitation about buying comics on their phones. To the new generation digital is going to be the way they read.
Hopefully DC and Barnes and Noble can get themselves together and work out their differences-- but I'd be surprised if it works out well.
Death knell for the Nook? The failure of DC's digital initiative? Probably not-- but it doesn't help.