Barnes & Noble sent out a press release last night explaining what had happened to the iPad app.
B&N decided to combine removing the ebookstore link with adding a new feature. They're probably hoping that the latter will be enough to get you to swallow the former (ditto for Amazon). Plus, I'm told it's a PITA to get an app approved so this way they can cut back on the pain.
The Nook iPad app is going to be coming back soon, and it'll be be getting access to 175 newspapers and magazines that B&N have been selling through NookNewsstand.com, including titles such as : Esquire, Maxim, Forbes, Food Network Magazine, Newsweek, Popular Science, ESPN The Magazine, Elle, O, the Oprah Magazine, Parenting: Early Years, The Washington Post, USA TODAY, The Chicago Tribune, The Los Angeles Times and many more.
These are the same titles that you've been able to buy for the NookColor since last fall.
P.S. The app still isn't showing up in the app store on my iPad, and I'm not exactly sure when it will be.