I think the real goal with moving to a platform such
as github is reducing
the entry barriers for new contributors. As it has been mentioned already,
almost all projects who moved from SVN with "send patches" contribution
system, to Git/Hg with Pull Requests have got non-negligible growth in
contributions.
I'm confused, maybe it's your use of a double negative (non-negligible), but that
sounds contradictory?
Are you saying that projects that have moved from SVN to git have had no growth or good
growth in contributions?
Ged.