From an enhancement request I put in to TMW 2 years ago: "I think that subplot puts too much space between the axes as well as between the axes and the edge of the figure. I would like to be able to control this. Looking at the code of subplot.m the spacing seems to depend on a field of the application data called SubplotDefaultAxesLocation and the hard coded values for inset on line 130. I believe if the hard coded inset was changed to a field of the application data, then a user could modify the spacing between subplots. Further, the defaults for both properties should become modifiable with something like set(0, 'DefaultAxesSubplot..."
As an immediate workaround you should be able to copy subplot.m to mysubplot.m and change the line which sets the variable "inset" to a value that you like and then change the DefaultAxesPosition globally
set(0, 'DefaultAxesPosition', ...
or locally
set(gcf, 'DefaultAxesPosition', ...
