Some people seem to have problems with the default delegations.
I think, because this way people can choose their own version of the tools, based on their own PATH etc. Conversely, some people seem to leave tools such as psselect in unsual places, generally not available when a2ps is run. These people would nevertheless like a2ps to find psselect. In any case, the default should be not to hard code the path. Default is not to hard code.