Akuperma, while I do not know of statistics, it makes sense that OTDs will want to preserve those aspects of their former lives that they enjoyed. Some, BTW, eventually come back (I personally know one), in some case to another stream of Orthodoxy (e.g. Chassidic to MO). As for not being distinguished from goyim, it takes several generations of assimilation to lose all of the little thinks (manner of speech, body language, etc.) that come from the national aspect that is not connected to free choice (see Rav Soloveichik, “Two Beritot”) make us distinguishable.
Joseph, I think he means the part about safek goy. However, if one holds like Rav Moshe 9an certainly at least b’diavad we do) if someone’s parents were not frum most likely the kiddushin was not valid. In fact, someone told me that before he became BT he was a witness at his sister’s wedding.