I believe "domains" are just to practice and improve coding skills. Hence, coders will perhaps download test-cases to further improve/correct their codes only (and not to cheat by hardcoding values). Thus, allowing to download testcases for 5 "hackos" seems a fair deal.

But "not revealing" test cases for "live" contests is pretty justifiable because contests are just a platform to compete with fellow coders. The ability to find fault in the code by enumerating different possibilities, is an extremely crucial skill for a programmer. This skill will be completely overlooked if the test-cases are visible, and ranking won't actually reflect the true potential of the programmer this way. Moreover, we also can't deny the possibility of people hard-coding testcases into solution. Hard-coding has been a serious issue ! This problem is one example where test-cases were guessable, and a lot of guys hard-coded the results into the code, inspite of the warning !!!

I am not aware what were the actual reasons for choosing such rules but this is what I feel ! :)