Cassandra cannot lose more than 10s of data because it will slow down writes as necessary to make sure it does not. That's why comparing to a system that allows arbitrarily high data loss is unfair.

People can and do run Cassandra with full durability. When people understand the tradeoff between performance and data loss on power failure, you'd be surprised how often they'll chose real durability. (And by batching concurrent writes into the same fsync, the penalty isn't nearly as high as it would be in a naive implementation.)