How popular would you say that SQL is compared to NoSQL?

Correct me if I am wrong, but it sounds like SQL already has ACID properties.  Why then, is it hard to join across multiple disks in a cluster?  

Why do so few NoSQL databases have ACID properties?  What is the drawback of ACID, assuming you are not the one who has to implement ACID?

I'm curious about consistency with NoSQL, specifically in the reading where it says:

""The same query might yield slightly different results depending on which server it goes to and other details. But in many applications, that doesn't matter""

Could you explain why a query might have different results depending on the server, and why that doesn't often matter?