I'm not completely sure that what you have said is accurate, but following a small amount of preliminary research, though I couldnt find any statistics for the last 3 years (most appear to be pre-2003), it appears that you might be correct (see the sources).
The most credible reason I found whilst (briefly) reading through various articles is the following:
""For both men and women, the No. 1 reason for becoming a vegetarian is for health benefits. Nearly half of all vegetarians cite health as the single most important reason for giving up meat. And because health concerns play such a big role when people choose vegetarianism, it makes sense that there are currently more female than male vegetarians. According to statistics compiled by Men's Health magazine, women visit the doctor an average of 6.2 times per year and men 4.5 times per year. One could use these figures to argue that women are hypochondriacs, but what they show is that women take a more proactive approach to their health.""
[direct quote from http://findarticles.com/p/articles/mi_m0820/is_n210/ai_16019829 ]
In short, many females are more likely to be pro-active about their health or sensitive (possibly, even susceptible) to the moral issues surrounding vegetarianism.
This follows from the 2:1 female:male ratio stated within the same article which i quoted from previously.
""The gender gap: if you're a vegetarian, odds are you're a woman. Why? - includes related articles""