It would be nice, if one could define the margin as a parameter in .matplotlibrc.
Seems, that there are a couple of questions on stackoverflow (see for instance http://stackoverflow.com/a/14498142) addressing this (maybe using 0.04 as a default value would also be an option).
Also it would be useful if somebody would like to generate his own theme (have a look at this stackoverflow question and the answers http://stackoverflow.com/q/14349055, look at the voting, seems that people are interested in such things).
added rcParam for x and y margin
Addresses issue #1766
@tacaswell thank you.
I think this ticket can be closed now.