There's a lot of rumors going round as to why.
Note this video http://www.youtube.com/watch?v=6Ud88fyLwc4 This is possibly the most accurate and helpful information on this.
MLG has said that there was collusion between the two teams before the match, basically match fixing, Riot supports this claim.
Curse has given an appology on youtube for having the ARAM game saying sorry to MLG and their fans for being unprofessional. However they have also said in a later video that all other accusations are false.
Dignitas have been silent as they get all their words together.