Presumably (or as I've been told by teachers) the reason women can't serve on the frontlines as infantry in the British Army is because they may distract male soldiers, but also because a male is much more likely to risk his own life by protecting a female than another male, and may make rash decisions that endanger himself, the women or his entire squad.
But according to a number of people I've spoken to who have been part of the Armed Forces, the reason behind it is because frontline infantry are much more likely to die.
And it looks much worse on the news, and for national and military morale, if a woman dies on the frontlines rather than a man.
That said, these days women can be frontline medics, where they're just as likely to be injured or killed, or can be assault helicopter pilots or any other sort of position, which are all exceedingly dangerous anyway.
I wouldn't be too surprised if Britain follows suit and eventually gives women access to frontline infantry. It'll raise debate, but it will probably be accepted.