We're obviously made of different stuff this side of the border, I have never seen nor heard of this being penalised.
Swinging people by their collar, certainly, but not being dragged down.
Even the NFL banned the practice, after a series of major injuries caused by its use:
The horse-collar tackle rose to infamy during the 2004 NFL season, in which it was implicated in six major injuries, four of which were caused by Williams, including two in one game. The injuries that season included broken legs for Philadelphia Eagles wide receiver Terrell Owens, Eagles quarterback Donovan McNabb, Baltimore Ravens running back Musa Smith, and Tennessee Titans wide out Tyrone Calico.
...
The horse-collar is particularly dangerous due to the awkward position of the player being tackled, who will often fall backward in a twisting motion with one or both legs trapped under the weight of his body. This is exacerbated if the player's foot gets caught in the turf and by the additional weight of the defender. Potential injuries include sprains or tears to ligaments in the knees and ankles (including the ACL and MCL), and fractures of the tibia and fibula.
http://en.wikipedia.org/wiki/Horse-collar_tackle