Gender and ethnic diversity is completely irrelevant to building software of good calibre. I don't see why people are so occupied with making everything multicultural and "diverse" nowadays. A diversity of minds might be useful for the kernel, but a diversity of physical attributes is just superficial and a red herring.
Do you have a citation? I'm not sure about software specifically, but here are citations that suggest that diversity improves financial performance, team performance and innovation:
Beryl Nelson (Google) had a talk in March at a conference called "Voices - Creating Global Connections":
Here are a few instructive slides from the first 7 minutes:
* Financial Performance: Companies with a higher proportion of women in their top management have better financial performance
..* from Georges Desvaux, Sandrine Devillard-Hoellinger, and Pascal Baumgarten: Women Matter: Gender diversity, a corporate performance driver, McKinsey Report, 2007; similar results in Catalyst study; and for differences in race, by Cedric Herring