Why does wheat matter?

CNN reports on the plight of a wheat-intolerant New Jersey girl whose first communion was declared invalid by the Church because the wafer was wheat-free. Obviously, this sort of incident is deemed newsworthy because of the Church's seeming defiance of common sense and compassion in refusing to allow an exception to an arcane rule. These and similar news reports share an unspoken, but unmistakable undercurrent, along the lines of, "How can an organization beset by problems as severe as the priest sex abuse scandal fritter away its remaining goodwill by alienating the faithful with such narrow-mindedness?" As someone who did not grow up Catholic, I admit that a good answer eludes me, and I'm hoping a co-blogger or reader might offer some insight. Why will the Church not allow the faithful to participate in communion using a non-wheat wafer when wheat would cause them serious medical harm?

Rob