The point that they might have to write seriously mathematical software is rather
invalid, in my personal opinion. Why don't you require medical/legal/linguistic/... knowledge too, then?
Mathematical studies in the field of computer science have nothing to
do with preparing students for writing mathematical software. It is
to provide students with the tools needed for the study, design, and
analysis of algorithms.
By using people who studied something more relevant to the type of
specialized software being written, the specific needs and problems
will be easier to capture, analyze and solve.
That may well be true, but that domain specific knowledge doesn't
help the programmer/designer figure out algorithms appropriate to
the task or to decide if certain approaches are even computationally