Currently the thresholds needed to get various 'powers' are absolute. The exact numbers vary depending on whether the site is in beta or not but that is not relevant to the point I wish to make.
A casual browsing of the beta sites suggests that voting patterns (i.e., how often people vote, how they vote up questions and answers etc) is different for each site. Thus, each site will have a different 'base level' of voting that reflects the number of votes cast by the average voter. Given the above pattern, it may perhaps make sense to actually have relative thresholds instead of absolute so that the thresholds 'automatically tune' to the level of voting that takes place at the site. Obviously, the specifics how this can be implemented need to be carefully worked out (perhaps, track the average no of votes cast and a multiplier of that should be the threshold? Have absolute thresholds till an average number of votes exceeds some number and then shift to relative?).
However, the question for now is: Should thresholds be relative?