Well, 100 extra damage right there. Unmitigated by armor, mitigated by nature resist...
Oh and the nerf is due to a programing mistake present in every "on attack" procs.
Basically, the proc damage would activate certain proc options like sword spec or lifestealing. In addition, it sometimes added extra damage due to heroic strike, which led to chains like "heroic strike, sword spec proc + heroic strike, thunderfury + heroic strike, random damage enchant (flaming for the proc rate) +heroic, sword spec + heroic, thunderfury + heroic, flaming +heroic" with all the heroic strikes ending up not costing any rage. Throw in a hand of Justice, and a Darkmoon fair card: Maelstrom, and you have an even deadlier chain proc. That's what they are removing. I think they should, on the other hand, increase damage enchants's proc rates because of the actual loss of power.
With my rogues I have seen horrible proc chains as well. But nothing causing as much damage as this one has.