NEW YORK (TheWrap.com) - TV networks can advertise, promote, and tweet endlessly in hopes of drawing ratings. They can offer a tireless parade of semi-naked people, guest stars, very special episodes, cliffhangers, "midseason finales," and any number of other old and new tricks in pursuit of ratings. They just can't try to directly influence the 25,000 or so Nielsen families whose viewing habits determine those ratings. Oprah Winfrey was reminded of that rule after she took to Twitter and invited viewers -- especially any with "a Neilsen box" -- to tune into her struggling OWN network. ... read more..