MPI still gets pulled in - this is an artifact of some recent changes to boost.graph (which is used by python) to optionally make use of the parallel graph lib depending upon some #define.
I see boost/graph/accounting.hpp includes boost/mpi/config.hpp. Is this the culprit ? Can't that dependency chain be broken up, to not have boost.python depend on boost.mpi ? (I think this is really a general question, not specific to boost.graph. I remember seeing a quite rediculous dependency graph generated by Troy Straszheim, and breaking out of this would probably be a good idea independently from whether someone tries to break out individual components or not. (It may well reduce overall compile time.)
There a bunch of other Boost.Graph files that include things from boost/graph/parallel which uses Boost.MPI. This was done to allow more transparent use of parallel graph data structures and algorithms, just by including <boost/graph/use_mpi.hpp>. -- Jeremiah Willcock