I just noticed http://arxiv.org/pdf/1507.03989v1.pdf (it's on todays HN). It claims that in Astronomy Python is used over twice as much as FORTRAN and even C/C++ is used more.
So the claim of "use" is really what the astronmer sees in their programmer- not in the measure of instructions executed.
Python/Matlab/IDL are important because it is easier to quickly write correct code than in C++/Fortran.
Had I written the paper (I'm a scientist, I work with astro data sets at times, and manage Python wrappers for Fortran and C++ libraries) I would have calculated this based on instructions executed, not lines of user-facing code.
After all, if the code the astro people called was Pure Python, they wouldn't use python, as it would be too slow.
#!/usr/bin/env python
from subprocess import Popen
Popen("/usr/bin/some-fortran-binary")
print("Once again python saves the day.")