Quoted from neurokinetik:
I'd just be happy if the games were level. There were as many unlevel games as there were level ones. This is certainly nothing new for these types of events, though.
The floor is a huge factor in the leveling. The Old Main Building that housed the show was built in the 1800's and even if the floor was perfectly level when new, it has had a lot of time and traffic to change that. The games got shuffled around for various reasons and they may have started out level but didn't stay that way.
Keep in mind that almost all of the games on the floor got more play in a few hours than what they had been played in years. No matter how carefully you go over your games, problems are going to happen.