> On the other hand, once multiple separate implementations are already in widespread use, there's immense value in working out a least common denominator of language features and standard library APIs that work everywhere

Yeah this was what I thought. I remember Valve Software wrote a paper about cross platform development and said it was useful compiling with Visual C++ and gcc to shake out any iffy syntax that worked in one but not the other. Of course with performance-critical code and code that needs to run on consoles as well there will always be platform-specific stuff, but if you can get 99% of the code working across multiple compilers that's pretty good.