Agree, Penrith are very good at it, I think the refs have been so conditioned to how they tackle 1 low 1 over the top and late 3rd flopper. When they get it wrong and the flopper is late it looks so similar to the norm they let it go.
Doggies have got it going this year (which is no surprise given the Penrith influence there) and look how it has improved there chances in games.