Aurora is more expensive, more so on the high-end, so it's not entirely clear that it is the best choice for all applications:

db.r3.8xlarge: RDS Aurora $4.640/h, RDS MySQL $3.780/h, RDS PostgreSQL $3.980/h

> Aurora is more expensive, more so on the high-end, so it's not entirely clear that it is the best choice for all applications:

> db.r3.8xlarge: RDS Aurora $4.640/h, RDS MySQL $3.780/h, RDS PostgreSQL $3.980/h

Based on your numbers the difference in pricing between Aurora and Postgres ($4.64 - $3.98) x 24 * 30 = $475/mo. To the company using a db.r3.8xlarge, which has 32-cores and 244 GB of RAM, that's not even a rounding error.

For many installations, an Aurora read replica can eliminate the need for a multi-AZ master instance which cuts the cost of your master instance in half.

The failover guarantees with RDS Aurora are substantially better as long as you have 1+ read replicas.

That alone is worth the difference imo.