There are plenty of free software contributors at Google (Ian Lance Taylor
and Guido van Rossum to name just two: a random grep of the changelogs of
any major plumbing component will find more although I suppose it's hard
to find many people who have the same sort of influence on anything that
Guido does on Python).
Of course if one considers GCC, the binutils and Python to be
insignificant or not plumbing enough, then maybe one can avoid this: but
any definition of 'plumbing' that excludes GCC and GNU ld in particular is
a silly definition.