It's not as random as awarding points for an arbitrary theme. It is much easier to judge a wedding photo as a wedding photo and a landscape as a landscape than it is to judge how a random theme like circles has been incorporated into a wedding photo. I wouldn't even know where to begin to judge theme incorporation but I have a good idea how I personally perceive and like different photos, and the technical side is even easier and more objective.
Well not really, if you can't see how the Wedding photo has integrated the theme of Circles then it has failed and would score lowly?
I think technical marking isn't possibly the best way for a general competition. I for one wouldn't be able to mark a photo on technical merit as that doesn't really interest me. I'm all about emotional response, so the old impact score I guess? A simple voting method is going to generate the most interaction?