It isn't common, that is for sure. And the bar code folks don't make it easy for folks. Simply publishing the bar code database would be a huge 'win' for barcode adoption.
[1] http://techcrunch.com/2014/02/04/how-a-startup-accidentally-...
I bet they built custom hardware for a couple reasons: 1. Custom hardware sitting around reminds you of Amazon and your ability to order. Having a new device feels more futuristic, which does seem logically odd. 2. Durability. While cooking etc, you dont' want to touch your phone. This looks very easy to clean/throw around. 3. Barcode scanner speed. Apps with cameras are much, much slower at recognizing barcodes than this. This removes a lot of interface. Just scan it and you're done -- no hassle switching apps, holding the camera just right, etc. I bet this feels more natural.
They have that: https://play.google.com/store/apps/details?id=com.amazon.pri...
Barcode scanner, and voice recognition. It's not nearly as cool or convenient as a dedicated device though.
Compared to a dedicated barcode scanner, phones are pretty terrible for this.