Redis and Memcached are not comparable. many application, specially such applications that requires extremely high scale, will actually use both Redis and Memcached.
Redis is single threaded and allows for atomic operations by design, it's a Key/Value store with a very complex set of datatypes being supported and above all that, data in Redis can be persisted and hence still present across restarts.
Memcached is much simpler (and powerful exactly for that) and is the perfect solution for simple Key to Text Blocks, it's ability to compress content allows for efficient storage of large quantities of large text blocks (such as full HTML pages), data is stored in RAM only and hence, perishable.
So, as always, plain benchmarking is in many ways a little miss leading.