By splitting the mount into two parts. They can accommodate devices of different width, in portrait or landscape mode (though you will have to decide which orientation before you finalize affixing your mounts.)
There is a smartphone version that can also accommodate tablets, but the tablet model, called the Koala, works best for larger tablets like the iPad.
Another way that Dockem has outpaced the competition is the mounting system. Instead of a permanent screwed in connection, they include genuine 3M Command adhesive strips and even offer water/heat resistant strips. This is of note to me, as I just real eased my JOURINAL app, which is meant to be used in a bathroom! You mount your iOS device on the wall and let the JOURINAL app speak the news, in Siri's voice. Plus, it's completely hands free, so you can talk to the app and ask for sports, world, USA, technology, entertainment or political news.
Finally they include a guide for the charging cable, which is an important consideration. Perhaps this is irrelevant for the nook or kindle, both of which work fine with the Dockem mounts, with their long lasting batteries.
All units are available in white or black, and the Koala tablet model can also be purchased in chrome. Starting under $15, you can afford to place them throughout the home or office. And if/when you get a new device, such as the rumored iPad Mini, you can easily remove and use the 3M Command strips to accommodate different sized gadgets.