People who tend to use noSQL use it specifically because it fits their use cases. Being divorced from normal RDBMS table relationships and constraints, as well as ACID-ity of data, it’s very easy to make it run a lot faster.
Consider Twitter, which uses NoSQL because a user only does very limited things on site, or one exactly – tweet. And concurrency can be considered non-existent since (1) nobody else can modify your tweet and (2) you won’t normally be simultaneously tweeting from multiple devices.