Oldest trick in the book and seems to be used even on Scirra arcade to create multiple accounts to keep your games at the top of the charts and down vote anyone's game that might compete against yours for a prize.
Arcades thrive by boasting of numbers of players online so they turn a blind eye to multiple accounts and this could easily be solved by requiring a reputation point system for anyone wanting to rank a game.
On Scirra they should require at least 500 reputation points or be a licensed developer to vote on any games in the arcade and that would end people making multiple accounts just to vote up their own games.
I seen that kongregate scam going on from the beginning so I don't even try to enter their events for prizes anymore. If you complain they will go after you like wolves and there are cliques of developers mostly from other countries besides the US that work together to vote up each others games so one of them ends up with a prize each time.