While memcache and redis are often compared, I don't think its entirely fair to compare them. Redis and Memcache have very different design goals. I don't think anyone is using memcache as a primary source of truth or wishes it has persistence. Memcache is a cache, Redis is a database.

Redis offers much more than Memcache, even it its at the cost of performance. The article assumes that everyone runs redis like they run memcached. They don't (http://blog.pivotal.io/pivotal/case-studies-2/case-study-how...) and if Salvatore were to fork memcached to try and get many of those features into memcached its doubtful the community would ever accept it. If providing those features came at the cost of performance, it would have been terrible for companies that actually depended on memcache being a fast in memory cache.

It isn't so much that "Redis is better" it is, Redis is more likely aligned with what you are trying to do and more flexible. However I doubt you could convince Facebook to replace memcache with Facebook, for any of the "engineering efforts" that were put into Redis. Likewise, I doubt Facebook would be running a fork of memcache that offered Redis-like features.