The National Health Service's Decision to Allow Heterosexual Couples Treatment

Why would it be acceptable for the National Health Service to help heterosexual couples but not homosexual couples? It may not be reasonable and especially as the present government has after all legitimized civil partnerships which are equivalent to marriages. If it just comes down to economics it's a pragmatic decision about how we use resources in the National Health service. I think there should be an age limit, a lower as well as an upper age limit.