1) Apple makes and sells everything itself at very high profit margins. They also work with some retailers to extend reach. Meanwhile, Amazon makes nothing (except the Kindle) and sells millions (billions?) of small items at a miniscule profit margin. Completely different models here.
2) Apple is notorious for not trusting other parties to do their business. Amazon depends entirely on it.
3) The parts of Amazon that overlap into Apple's interests -- digital content and AWS -- are irrelevant. Apple already has a huge content distribution channel, and does not need the help of Amazon's agreements with creators. AWS could be intriguing, but if Apple thought AWS was worth using, they'd already use it for iCloud, iTunes, etc.
While Apple and Amazon are two of my favorite companies in the world, I see very little that would give way to a potential acquisition.