I'm afraid these folks are wrong in one respect.
In most cases, there is a way to determine a programming language (or at least a compiler) based on an exe's signature. Each compiler, packer, and exe modifying tool has a unique "fingerprint" that it leaves on a file. Most of these tools are found in the rather shady "underground" scene where the reversers and crackers hang out (since it's necessary to know what sort of packing has occurred on a file before you attempt to reverse engineer it). One such tool which I regularly use is called PEid. You can google it but make sure you run a thorough virus scan (http://virusscan.jotti.org/) on whatever you download since you'll almost certainly end up at some rather shady sites.

As for the other points, they are pretty much spot on. Almost any language can be used to do almost anything. Furthermore, most languages can be combined (through the use of inlined code, DLLs, etc.). It's really just a matter of what you want to do and how hard it will be in a given language. For most rally simple projects i can throw something together quickly in VB that will do the trick, but most (if not all) more complicated programs will be written in C or some variant of it (C++, C#, etc.).