You are drawing a wrong comparison. Your Carling Cup might well see replacements, but it won't suddenly see them play handball. These players could easily be substituted and no one would bet an eyelash, as long as it was communicated beforehand.
Similarly, matchfixing is being looked at quite severely in several sports, such as Boxing and Football. This should be no exception.
They broke the MLG rules by
1) agreeing to that ARAM beforehand
2) agreeing to (allegedly) split the prize money.
If nothing else, MLG needed to set an example that people shouldn't be dicking around when there's a sizeable amount of money at stake.