G-Dub is trying to give them a little kick, upping their attacks in the new errata. I can only assume the Chaos Marine variant will get these as well (although IMO what they really need is more resiliency to stick around long enough to get into h2h).
My terrain is cruising along well, so I took a break from it to make this thing. To give him two power fists I hacked off the thumb on a spare one I had and switched it to the top of the fist with some green stuff. A lot of the other parts for it come from the Maulerfiend and Chaos Spawn kit. The taller legs give him a much more menacing pose I think. As always, Green Stuff Industries tentacle maker comes in handy!
One thing I'm experimenting with is some cracked armor texture, using Agrellan Earth. It looks really good at this stage, just hope it survives once I prime it. If it works good I'll probably use it on some Plague Marines I'm looking to build in the near future.