As I understood it, SQL was a language for describing the Relational Algebra which was a closed mathematical concept.
You can take the syntax, assign functions to produce output from a non-relational model, but it's no longer SQL...and it's underlying power (the closed Relational Algebra) is no longer present.
So in a sense syntax and being relational are orthogonal, but syntax isn't the defining characteristic of SQL (or why it's so powerful). I think a more insightful statement is: SQL (Relational Algebra) and being relational are codependent and relational and non-relational are orthogonal.
Which, if I am not mistaken (and again I am still trying to understand the finer points which is what motivated my original comment), NoSQL people fundamentally _cannot_ offer a query language similar to SQL based on the closed relational algebra.
They can mimic the syntax to make it more intuitive for new users coming from traditional RDMBS environments, but it's fundamentally _not_ SQL/relational algebra.
But again, I am just a cursory admirer/learner and I am still trying to iron out my own understanding of the underlying theory. So all additional information/clarifications welcome :)
You can set up non-relational data structures in SQL. You can set up a relational data structure in virtually any programming language.
However what the NoSQL people are learning is that smart developers really want relational models. So they are offering the features that can be used to achieve that.