You presume syntax is like fashionable clothes all decorating the same basic thing underneath; that's not at all true. Syntax is a reflection of the underlying differences in semantics of these languages, they're not just decoration.
You can write procedural C style in any language, but you're not really using the language if you aren't using its idioms which will inevitably reveal the reasoning of its syntactical choices. Lisp is a perfect example, as is Smalltalk.
I explicitly talked about minor syntactic differences between curly-brace languages, not about Lisp or Smaltalk. Switching from one curly-brace language to another generally doesn't involve any deep paradigm shift, it's essentially just memorizing a bunch of irrelevant syntax differences. If I have some procedural C style functionality implemented the same way in languages X and Y (happens pretty often), having the code 95% identical is missing out on the nice things that I could have if the code were 100% identical.
It's true that the Java runtime and the C# runtime provide different services. But the same is true for databases. Oracle's feature set is different from PostgreSQL's. Yet the database community got its act together enough to standardize the syntax for basic features at least, so you don't have to relearn inner joins when you switch, and you can mention "SQL" in job openings and be understood. (I wonder if the NoSQL community ever gets smart enough to do the same?)
Choice of syntax affects how easy it will be to create tools for the language (IDE syntax highlighting, code browsing/navigation, automated refactoring, etc). There is still plenty of room (and need!) for improvement, for innovation. At the other extreme, imagine a world where every language used C++'s syntax.
There are more differences between steel-toed boots, sandals, and stiletto heels than just how warm they are. In modern times it is also rather rare to encounter individuals wearing togas and/or powdered wigs. I'm not convinced that fashion is a complete explanation for these phenomena.
You can write procedural C style in any language, but you're not really using the language if you aren't using its idioms which will inevitably reveal the reasoning of its syntactical choices. Lisp is a perfect example, as is Smalltalk.