as much as a deposit/prepay system would help assure attendance or commitment to an event, wouldnt it also mean a new increased logistical facet to a host's list of things to do?
could public scrutiny into "repeat offenders" resulting in a public list of chairsofters after x no shows or making a list of people that belong to a default "tentative" list help? ie, you bail or no show x number of times or show a repeated pattern of such behavior and become a permanant "tentative" for any game that you post as "in".
not to say that there arent any number of legitimate reasons for one to not make it but to not inform people or not to acknowledge such an action publically is....inconsiderate to say the least. one can hardly be LEET if one never shows up to be leet. it could even be given some humiliating name like....ummm.... the list of Politicians since they make promises that they dont keep on a regular basis.