[plorkyeran]

"Supports AVC" doesn't mean a great deal on its own. H264 has a number of different profiles (over 20, although only 3 are commonly used), and 20 different levels. Most of the potential combinations aren't relevant, but supporting the full range of hardware decoders while also sending something reasonably close to the best quality that the device supports can mean encoding ten different versions.

If it's a particularly low-end/old device, Amazon may have simply decided it's no longer worth encoding a version supported by your device's hardware encoder, while Netflix still does.