What’s “Barnes & Noble?”
A bookseller. They are saying that WinRT may have the Barnes and Noble "Nook" e-reader software built into the OS, thus allowing them to compete against the iPad (iBooks, Kindle and Nook e-reader software) as well as the entrenched Kindle and Nook e-readers.
I flatly do not know if the Kindle supports the Nook e-reader, or if the Nook allows you to load the Kindle e-reader software (although I doubt they would). I do know that neither the Kindle nor the Nook have iBooks (Apple's e-reader); and that the Apple iPad has apps availble for Kindle and Nook.
Kinda surprised that MSFT isn't hopping on the book retailer bandwagon like Apple did.