We don't cause a fuss just when the proportion is not exactly right. We cause a fuss when the proportion is way out of whack and obviously wrong. When like less than 3 percent of Boston Ruby programmers are women, something is blatantly wrong. There are probably more factors at work than mere spontaneous career preference that are causing this seriously skewed distribution.
This is not just an abstract inconvenience either. Whenever you are part of a historically marginalized minority -- whether by color, gender, or nationality -- it will likely be more uncomfortable for you to enter fields where you are the only person from your group. This is particularly true for women.
Not only are sexist comments more likely when there are not a lot of women at events (see http://www.ultrasaurus.com/sarahblog/2009/04/gender-and-sex-...), the women will also likely feel more uncomfortable because of the disproportion. Let me quote a posting on our outreach mailing list thread from a woman to elaborate:
"I have definitely never experienced anything threatening or offensive at a Ruby group meeting. But, you show up at an event where there are 50 men or more to 3 women, and you grow to expect some double-takes. Some women, like me, are okay with that. A lot aren't. And it makes it hard to show up alone or when you don't know anyone if you know you're going to stick out like a sore thumb. A man can show up at boston.rb for the first time and not have anyone pay the least attention. A woman cannot.
"There's some critical mass that needs to be reached before that's not true anymore, and it's just hard work to get there. There needs to be enough women who don't care if they stick out, so the women who do care don't stick out so much. And you need to make plans to meet the women you know there, so they already know someone. That could be a component of any project night, outreach, or mentorship effort -- encouraging people to come to the meetings, and affirmatively planning to meet them there."
I hope these points carry at least a little weight for you. Thank you for raising the challenge.