How do you know a platform has made it? Angry Birds

OK, exclusive Angry Birds -- and, in this case, they're good for the old platform, too.

Earlier today, Barnes & Noble announced availability of exclusive Angry Birds unlockables, including Mighty Eagle, free for Nook Color. Consumers need three things: The tablet, game app and to be physically present in a Barnes & Noble store.

The book seller is doing what rival Amazon can't -- cross-promotion from its 700 physical stores and gameplay on Android. Amazon doesn't have the shops, and Kindle doesn't have Android chops.

Barnes & Noble also will offer Angry Birds branded stickers and other collectables inside its retail stores. It's a plan for pulling e-book readers into the book shops where they might, gasp, buy something printed on paper.

"We've already experienced great success with Nook Apps and Angry Birds as our bestseller", Jamie Iannone, president of B&N Digital Products, says in a statement. "We invite all Angry Birds fans to visit our in-store Nook Boutiques to try this fun experience on one of our many Nook Color demonstration units".

That's the other purpose getting people into stores and cooing over Angry Birds -- selling more Nook Colors.

However, Angry Birds creator Rovio isn't stopping with Barnes & Noble. Peter Vesterbacka, Rovio chief marketing officer, says in a statement that this is the "first step towards taking Angry Birds to physical locations around the world".

Barnes & Noble's timing makes sense, with summer coming. Kids are out of school (and playing games), and many adults may be looking for an e-reader to kick back on those humid nights and vacation days. Yesterday, Pew Internet revealed growing demand for e-readers, with ownership among US adults doubling to 12 percent over six months. Nearly one in four Americans with household incomes of $75,000 or more own an e-reader.