Well, first thing is that most new code in scientific research is developed in PhD projects which last some three or maybe four years. The people who develop this do not have resources and time to maintain this code. Projects don't have a budget for that. There are projects which are very long-running (think CERN or ESO's VLT) but even there the true duration of the code usage is seldomly planned (AFAIK, ESO VLT has just started to transition from Tk/Tcl to Python).

You could say then, "well, then Python is perhaps just not a good match for those pesky scientists".

And this brings up two more points:

* A lot of important tools and libraries in the Python ecosystem was developed by scientists. Numarray/Numpy is a good example.

* If the core Python developers don't have the intention to maintain a backwards-compatible language version for more than, say, 15 years, they should perhaps clearly state on the python.org main page something like: "great, as you are a scientist, we welcome your contribution, but Python might not be suitable for tools that support long-term research".