Agreed. If performance is the main (or an important) criteria for the competition then the choice of language is rather more significant.
If you have only 1-5 seconds of computations time you're going to choose for a compiled language every time
In any case, I see both python and ruby on the page you linked to, so perhaps I'm missing something.
and on that page it says:
Each submitted source program must be written in C, C++ or Pascal, it must be smaller than 100 KB, the evaluation server must be able to compile it in less than 10 seconds and at most 256 MB of memory. No other extensions different than the ones listed above will be run.