Perhaps because the eMagazine is being generated by the publishers of The New Yorker instead of Barnes and Noble?
Computers and Android devices often also have the ability to run PDF readers and a reader from Amazon. Unless you sideload content through a computer and a USB cable a B&N hardware reader can only acquire eBooks and ePeriodicals from the B&N store. There's more economic incentive for B&N to update the software for the current hardware readers. The ePeriodical publishers might be inclined to include tables and images which aren't compatible with the older software readers and even the eInk hardware readers.
The corporate strategy is even more incomprehensible than you think because B&N barely supports its own magazine format on the NC and NT devices. The recent 1.4.X software causes the reader software to truncate the top "inch" or so of the magazine page during pinch-and-zoom in portrait mode.
For magazines such as "The Writer" with pages that have a small top margin this means that the top line or two of text is essentially not readable without switching to landscape mode first. For magazines such as "Guitar World" that often have pictures or captions extending all the way to the page boundary ... well you get the idea. This bug has existed for nearly four months and should be a trivial fix. Customer service will recommend all sorts of time-wasting troubleshooting (archiving/unarchiving the magazine, performing data-killing hard resets, etc) that will not fix the half-baked B&N nook software. (Software that's outsourced to Russia?) I am fed up with spending $20 per month to read digital magazines on expensive nook devices with firmware bugs that interfere with reading and may or may not ever be fixed. And each new (forced) update often introduces new bugs that range from annoying to killing compatability with your particular wi-fi router or even wiping out all user data.
The nook itself as a device is great but nook as a service is terrible IMO. After purchasing a N1E 3G, two NC's, a NST, and nearly $1000 worth of nook books/magazines for the household I am certainly not going to purchase another nook device unless B&N clearly and substantially improves the nook service. (Fool me once shame on you, fool me twice ... or three times shame on me.) All three devices have obvious but longstanding and annoying "reader" bugs, using nookbooks or nook magazines, that indicate B&N as a company is currently not capable of providing a superior e-reading experience on the nook devices. I have not noticed or found any obvious or annoying reader bugs with the "Kindle Keyboard" device so maybe it's time to try e-magazines on the Kindle Fire.
The Netflix app works great though so I will still keep my NC e-reader for watching stale television from bed.
They have changed their formating and I wish they would say where it's available before you buy an issue of a magazine. I've bought Newsweek magazines before that could be read on my iPad. However, I just bought an issue and after I downloaded it I get the "only supported on Nook tablet" crap. As to another poster who asked why B&N would support the Nook app on a device that is not an nook, why not, they wrote it! They are in the business of selling books, et al. That is where they make their money. They are selling devices so that someone who does not already have a generic tablet will get theirs instead of getting a Kindle. Basically, they have nooks because the other guy has a device. The sell them dirt cheap because it's not about the device, it's a means to an end, selling books. That is why they have always had apps for other devices, because it sells them MORE books/magazines/whatever. That is where they make their money. But they need to support the whole eco system better. I actually have a Nook color but pretty don't use it and use my iPad now. Mostly because I use it for other things as well and no point in constantly switching devices. I expect to read my media on either. Obviously the iPad is a better device, but the nook is good for various reasons as well. All their stuff has issues, devices and apps. They also seem to ignore their customers in these forums. They even kind of hide the forums. They gone from being easily found to being buried so that someone who doesn't already know they exist probably isn't going to find them. Just sad!