Keep in mind that a lot of people are 3 healing the 10 man on all fights. I'd be willing to guess that most of the people saying Disc is good in 10s are 3 healing and have a Druid. In that case, Disc is better. Not that 3 healing is needed in ICC10 (exceptions for a couple hard modes, Lich King, Dreamwalker and Sindragosa).
Lots of people make their in game decisions and get their experience in bad group compositions, so it looks like they're on some kind of amazing new drug to people who are in good groups. There are some other times when Disc is great in 10s, but if there is a Paladin involved you should almost always be Holy.