Not every bit is the same on AWS when it comes to AWS services, a quick plot below tells the story.
EMR is mostly based on community based Apache BigTop release with AWS’s own patches. It is unclear why the curve drifting on higher vCPUs counts, especially when considering Hadoop can scales to multi-cores. The margin is noticeably lower than others, probably due to the volume sale effect.
ElasticCache, leveraging Redis and Memcached, appears to be more of an deployment optimized service. AWS mentions nothing more than better usability on ElasticCache documents, so I assume AWS doesn’t change Redis or Memcached. 36% hike is quite something, when compared to less than 20% hike from using a 3rd party OS. The pricing linearity puzzles me, especially when it comes to Memecached, which is known for sub linearity with more threads.
Aurora commands a winning 74% hike. Aurora is AWS’s private MySQL fork, with multiple enhancements, spanning from storage, network, and clustering. Percona has good blogs on Aurora. It appears to me Aurora benefits from internal AWS APIs to build these enhancements and thus is able to beat others that just use EC2 instances.