I dont see why you should limit the quantity of photo's that a person can submit. Everyone gets the same amount of time to enter and if you are entering a photo it means you have the oppotunity to enter more. Entering several photo's doesn't mean you stand more chance of winning as all that is required to win is one entry. Beckys photo from the last comp was an imaginative well thought out photo with great composition. Likewise Jono's video showed that the video as a whole had been considered., the use of effects and music really brought it all together. I dont know if they submitted other entries but they only needed those to win.
People should be more concerned with the quality of their own entries and less concerned by the quantity of others