Titus Chalk recently took a fresh look at the 15+year old question of why tournament Magic contains so few women (article can be found here, http://www.mananation.com/women-and-magic-the-games-lost-tribe/).
The article is well written and contains many valid points about the gender gap in tournament Magic, but the article makes no mention of the body of research that does a lot of work to explain the gender gap.
There is a real gender difference in competitiveness (and performance in competitive vs. casual settings). Just as an example (I encourage Googling and/or looking up citations within this article for those with an interest), this recent article discusses the gender difference in competitiveness in the context of desire to enter tournaments: http://www.stanford.edu/~niederle/Niederle.Vesterlund.QJE.2007.pdf
Here's the abstract of the article:
"We examine whether men and women of the same ability differ in their selection into a competitive environment. Participants in a laboratory experiment solve a real task, first under a noncompetitive piece rate and then a competitive tournament incentive scheme. Although there are no gender differences in performance, men select the tournament twice as much as women when choosing their compensation scheme for the next performance. While 73 percent of the men select the tournament, only 35 percent of the women make this choice. This gender gap in tournament entry is not explained by performance, and factors such as risk and feedback aversion only play a negligible role. Instead, the tournament entry gap is driven by men being more overconfident and by gender differences in preferences for performing in a competition. The result is that women shy away from competition and men embrace it."
This gender difference is what I believe accounts (in large part) for the male/female ratio in tournament Magic. Comparing the field of any tournament to a figure such as "28 percent of people who play video games are female" is misleading. Women's reluctance to enter tournaments doesn't necessarily reflect a deficiency in Magic or an oversight by its creators or by tournament organizers.
Whether or not you enjoy competitive-level tournament Magic comes down to one thing: do you enjoy competing against and beating a complete stranger at a game. Not "do you enjoying playing a stranger." The joy must come from the (often intense) competition, otherwise FNM and the kitchen table provide everything you need, all without the car ride out of town and the $100 Jaces.
Entry into the tournament is not only optional, it's costly. Timed rounds, rules infractions, no take-backs, crowded spaces, entry fees, cutthroat deck construction, expensive cards, travel. Why are boys more interested in putting up with all this? Because they get more out of it. That's why they'll put more in.
Everyone enjoys beating their older brother at something, and many boys and girls enjoy beating their friends, but I think when it comes to being paired against a stranger and playing to win, the dynamic changes. Tournament Magic isn't about casting a cool Dragon or Vampire, or the laughter or joking that occurs as the games play out. It's about winning. Again, it isn't Magic that is this way, just tournament Magic.
Like many others, I think the Magic community can work to be more accepting and friendly toward female players that do choose to enter tournaments. However, we should be cautious (and look at the research) before we blame a harsh, male-dominated environment for having created a harsh, male-dominated environment.