>>28No, not all programmers are implementers of programming languages they program in. The proof of that is that the number of popular languages' implementations is much less than the number of programmers of those languages.
Many languages have several implementations, and many languages can be compiled with different compiler options that change the execution of pure, high-level code (for instance, in order to optimize it). For example, C code compiled with "gcc" will execute differently than code compiled with "gcc -O2".
And if you visit the Land of Total Languages, things will get even stranger: code in such languages produces the same results when executed call-by-value as when it is executed call-by-need, which is an even more drastic change of the execution model than optimizations or using a slightly different compiler.