All iPhones have good enough optics to detect 2D barcodes like QR Code. Linear barcodes like UPC were trickier until the iPhone 3GS, which has variable focus camera hardware that also admits direct access to camera frames. On the 3GS, barcode scanning is a cake walk.

There are many surprising things about RedLaser's success, but technology isn't one of them. I agree with OP that apparent violations of licensing (access to Amazon.com via mobile is not allowed) are surprising. Most surprising to me is how well RedLaser has sold given that barcode scanning was antiquated over a year ago by products like SnapTell. Why scan a UPC code when you can just take a picture of the cover of a book and have the product found just as fast, with as good or better accuracy? No matter if your photo is blurry, or badly lit, or out of focus, or only grabs a part of the book's cover...