There's a wide range of performance with storage systems but why are you comparing that to RDS? That's a managed database service that just runs on EC2 instances with EBS volumes, and EBS is designed for affordable and scalable persistence instead of extreme performance.

EBS is not your typical SAN, which usually offer much more throughput, IOPS, and reliability in exchange for more complexity and latency, however you probably won't even notice that latency if your SAN system is close enough and using highend links.