I choose every language I use based on the expressiveness of the syntax. What other reason is there to choose a language?
Some even says that the number of programmers available on the market for a language is important. I don't think it is a good reason but a related one is: your existing user base is composed of companies and consultancies with their own programmers; you can't abruptly choose a different programming language than the one they know.
I agree with you about the 'platform' of a language, though. That's one of those things that you can't get away from.
Most languages today offer the same semantics - first class functions, objects, namespacing. Apart from that core, there isn't really a huge variance except for fringe languages that, generally, have severe syntactical limitations as a result.