This is a lot of different things to different people. Each person that views the manifesto will come away with something different. This is the whole point.
Basically there is an abundance of great gaming material out there, waiting to be used. Why limit yourself based on what’s hot, new, or old? Almost every game system devised has a place in the rules that tells you to do with the rules as you see fit, take what you like, leave what you don’t, and have fun.
Yet so many of us just plod along with the rules as writ (which is well and good if you like all of them), even if there is a rule that makes the game less fun. The thinking here I suppose is that if the designers included it then it must have a purpose. The rule or rules in question might serve a goal, but if you don’t agree with it then why not change it. Game designers are not gods, their rule is not beyond question.
Also, you shouldn’t feel guilty about enjoying something. EVER (at least within the confines of a structured game). If you and your group are having fun then bag anyone who says you are doing it wrong. If one guy joins your group and bemoans the game you are running then it is time to part ways, because your fun is obviously not his fun. To each their own amusement, and really that is the aim here with all these funny dice.
For instance, I don’t care for FEATS. (ala D&D/Pathfinder) so why not just run the game without them? Another example is Colonial Gothic, I bought it over a year ago and haven’t played it or thought about it. Why? There is a mechanic that I find purposeless even though I like the setting and style, I should hack that.
That’s what this ideal means to me.