Just to clarify: I don't eschew RDS because of outage issues, I use RDS because it's much easier to set up and manage compared to doing it yourself.
To be honest, I didn't know RDS was backed by EBS but it makes little real difference to me as long as the backup procedures are rock-solid and the performance is acceptable.
Also, on EC2, EBS-backed instances boot faster [2]. Of course, you can (and should) still treat EBS-backed instances as expendable.
[1] http://aws.amazon.com/rds/faqs/#hardware-scaling
[2] http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/Component...