The world doesn't seem to agree with you. Straight from Wikipedia [1]:
Gender is the range of physical, biological, mental and behavioral characteristics pertaining to, and differentiating between, masculinity and femininity. Depending on the context, the term may refer to biological sex (i.e. the state of being male, female or intersex), sex-based social structures (including gender roles and other social roles), or gender identity. ... the meaning of gender has undergone a usage shift to include sex or even to replace the latter word. .... Gender is now commonly used even to refer to the physiology of non-human animals, without any implication of social gender roles.
>The modern academic sense of the word, in the context of social roles of men and women, dates from the work of John Money (1955), and was popularized and developed by the feminist movement from the 1970s onwards (see Feminism theory and gender studies below). The theory was that human nature is essentially epicene and social distinctions based on sex are arbitrarily constructed. Matters pertaining to this theoretical process of social construction were labelled matters of gender.
I think most places people hear it is that gender is the male/female/other self-description, and sex is the physiological state.
Most transgender social justice warriors or gender studies majors maybe. Not most people in general.
The vast majority of the people out there don't distinguish between gender and sex. Especially since only about 0.5% of the population identifies as a gender other than their physical sex.
There's a lot of terminology that the vast majority of people understand poorly. By itself, that hardly seems a good reason for a (supposedly) scientific magazine, particularly when using 'sex' exclusively would understood by everyone.
It probably comes down to the fact that the people practicing physical "hard" sciences do not particularly care about or trust the conclusions drawn by the "softer" sciences (sociology, gender studies, psychology)
Gender is the range of physical, biological, mental and behavioral characteristics pertaining to, and differentiating between, masculinity and femininity. Depending on the context, the term may refer to biological sex (i.e. the state of being male, female or intersex), sex-based social structures (including gender roles and other social roles), or gender identity. ... the meaning of gender has undergone a usage shift to include sex or even to replace the latter word. .... Gender is now commonly used even to refer to the physiology of non-human animals, without any implication of social gender roles.
[1] http://en.wikipedia.org/wiki/Gender