The majority of the corruption issues with MySQL comes from using the innodb engine. AWS built their own MySQL engine called Aurora that I would be shocked if Netflix wasn't using. It's designed for distributed workloads and should be harder to corrupt.

I'll admit I'm confused about picking Cassandra as well, but not for the same reasons you are. They're only storing subscriber data (billing address, subscription type, etc). That data is going to remain static for months at a time. When changed the only potential problem that could occur is the billing process using old data, but I'm guessing their system is smart enough to try again in thirty minutes.

Oracle may be fast, but it's also expensive. This is billing, which means batched jobs running in the background- they don't care how long each individual transaction takes, and I'm positive it's going to be cheaper to roll up more servers to compensate than it is to pay Oracle's licensing fees.