The following is from the NAC-Acts commentary (John B. Polhill, p.330-31). So as to fill out the discussion of this thread and give a little background to the development of the "Western Text" tradition:
When looked at closely, all four of these [decrees of Acts 15:19, 20] belong to the ritual sphere. Meat offered to idols was an abomination to Jews, who avoided any and everything associated with idolatry. "Strangled meat" referred to animals that had been slaughtered in a manner that left the blood in it. Blood was considered sacred to the Jews , and all meat was to be drained of blood before consuming it. The prohibition of "blood" came under the same requirement, referring to the consumption of the blood of animals in any form. These three requirements were all ritual, dealing with matters of clean and unclean foods. The fourth catagory seems somewhat less ritual and more moral: sexual immorality (porneia). It is possible that this catagory was also originally intended in a mainly ritual sense, referring to those "defiling" sexual relationships the Old Testament condemns, such as incest, marriage outside the covenant community, marriage with a close relative, bestiality, homosexuality, and the like. It is also possible that a broader meaning was intended including all illicit "natural" relationships as well, such as fornication, concubinage, and adultery. Gentile sexual mores were lax compared to Jewish standards, and it was one of the areas where Jews saw themselves most radically differentiated from Gentiles. The boundary between ritual and ethical law is not always distinct, and sexual morality is one of those areas where it is most blurred. For the Jew sexual misbehavior was both immoral and impure. A Jew would find it difficult indeed to consort with a Gentile who did not live by his own standards of sexual morality.
The four requirements [of Acts 15:19, 20] suggested by James were thus all basically ritual requirements aimed at making fellowship possible between Jewish and Gentile Christians. Often referred to as "the apostolic decrees," they belonged to a period in the life of the church when there was close contact between Jewish and Gentile Christians, when table fellowship especially was common between them. In a later day, by the end of the first century, Jewish Christianity became isolated into small sects and separated from Gentile Christianity. There no longer existed any real fellowship between them. The original function of the decrees no longer had any force, and they tended to be viewed in wholly moral terms. This tendency is very much reflected in the textual tradition of Acts 15:20, 29 and 21:25, particularly in the Western text, which omits "strangled meat," adds the negative form of the golden rule, and reads "idolatry" rather than idol meat. There are thus four moral prohibitions: no idolatry, no sexual immorality, no murder ("blood" now viewed as the shedding - not consuming - of blood), and "do not do to another what you wouldn't wish done to yourself."[End quote. Material in "[ ]" is Bobcat's for clarity.]