For many years the Chief Rabbinate had to approve all conversions, making sure that they were performed according to halachah. From the time this law was adopted there has been an effort to add the words according to halachah to all conversions.
Non-Orthodox demoninations have complained that their converts are "discriminated against" but opponents of non-Orthodox conversions maintain that there should be only one standard for conversion--allowing non-Orthodox conversions is a guarantee there will be no standards.
Thanks again, that's a very concise explanation.