When speaking in terms of "the average producer", are you talking about authors specifically, or publishers? My guess would be that the average age of published and active writers skews higher than 20s, and maybe even above the 30s. So it would put most writers in line with publishers who are used to dealing with B&N as a distributor.

I haven't noticed a difference in variety. I can't really recall a situation where there was something available on Amazon that was not also available on B&N. The exception could be for self-published authors who have foregone options to make their books available elsewhere. (I just looked up one self-published author I know of and it was available for the same price on B&N.)

It might be an age thing where younger people, who are more likely to self-publish, coming up will probably not strongly associate B&N with books. Borders(RIP) and B&N are older national chains.

But my own bias pushed me toward getting a Nook. I have a slight distrust for Amazon's platform being less open, and Amazon becoming too powerful because they're so good at what they do. I think consumers , writers, publishers, and even the economy are better off if there is more competition. (Not that Nook is overwhelmingly superior when it comes to being open since I ended up rooting mine.)