A few reasons Python is gaining ground in academia. Firstly, Python is _great_ for teaching undergraduate programming (see [0] for a good perspective), and many institutions are only now catching on and migrating from Matlab. Secondly it is a charitable language allowing scientists to concentrate on their research and not the CS implementation they are using. It is easy to learn, flexible, has lots of scientific libraries, interfaces to fortran/C libs. Julia is supposedly the future with speed being cited as the primary advantage[1], but it far from taking over. From a preliminary investigation into Julia it had less lib support, but most importantly, less inertia. The popularity and relative 'newness' of Python (compared to fortran/C) has meant that docs, blogs, forums, stackoverflow allow anyone to get involved and quickly overcome beginner hurdles and learn best practices. Finding which module interface for a C lib is easy. Comparatively, finding information on Julia's library support is much harder. As to why not use Fortran/C - well, if I need to suddenly share part of my data in JSON, make a plot in matplotlib, or generate a PDF/website for my data all the tools are easily accessible.
Python often gets a bad rap for speed, but this is rarely the problem it is made out to be. Python is best when used as a high level manager sitting on top of low level routines written in C/Cython. Following best practices means I do not a deep understanding of how compilers work to speed up my code, I just need to know how to pass off my data to an existing routine interfacing with LAPACK/BLAS or what have you where some really really smart CS people have already done all the optimisation.
Finally, it has a massive advantage over many other languages: Great documentation and a large community. This gives Python an inertia that the Go and Julia can't achieve yet. Julia, Go, and Closure all have dedicated communities (based on the number of mentions on HN), but the size of the community and their distribution biasing developer interests mean the barrier of entry is higher.
As these languages and their communities mature and grow, Python's advantage might diminish, but then we will just have more tools to choose from, and that would be great.
[0] http://lorenabarba.com/blog/why-i-push-for-python/ [1] http://julialang.org/benchmarks/