Umm...not entirely true.
A group of guys from my hall, all friends of mine growing up, used drugs. First time they just got reproved because they were sorry. A little while later, a year or so, they all got caught again. All of them denied any involvement, except one. He confessed. While there was no hard proof that they had used again (tho it was pretty common knowledge among everyone our age that they were using), the rest got off scott-free. Meanwhile the one who had confessed did so with many tears begging to be forgiven. Since he had already been in trouble with this once before they found that he could not really be repentant...(addiction and abuse are apparently seperate matters) and so he was disfellowshipped.
The moral of the story, and the lesson learned, at least in our hall is, NEVER CONFESS! DENY EVERYTHING!