This isn't just some annoying data collecting that the government is doing. It has implications having to do with the persecution of Christian and other religious minorities in Turkey.
I have a friend from Istanbul. She once told me how before they came over here, her parents wanted to make some modifications to their house. So she and her brother went to a government office to get the records for their house. They gave the clerk the Turkified version of their name, which was their legal name over there. The clerk went into another room, spent a very long time there, and came back saying he could not find the records. So then my friend's brother told the clerk to try the Armenian version of the name. The clerk said something like, "Oh, you're Armenian. You should have told me that." Then he went into a different room than the one he originally looked in, and came back with the records.
Basically, the Turks keep the records for the religious minorities separate in case they want to "deal" with them, like they have before in 1915, and other times of ethnic and religious cleansing. Turks, Armenians, Greeks and Jews don't look that different, and everyone over there speaks Turkish and has a Turkified name. So how do you find them when you want to get rid of them? You keep separate records for where they live and use codes so they can be identified.
It may sound paranoid to those who have no experience with the Turks; But those whose families have suffered religious persecution under them have no trouble believing this.