I'd also say that SciPy does this much better than the Python math library could ever hope to (without that math library effectively becoming a copy of scipy.special). It probably wouldn't be long before a user of the new Bessel functions also wanted Bessel functions of half-integer order (which turn up in statistics and in spherical harmonics problems), or of arbitrary complex order, or modified Bessel functions, or Airy functions and elliptic integrals, or ... For all those cases, SciPy has you covered, but extending the math module to cover all these things would be a lot of work and an unnecessary (IMO) duplication of effort.