Why? It's derived from GPL'd code, therefore it cannot be legally prevented to be distributed by anyone that gets it.
GPL code doesn't allow you to redistribute someone elses work after they send it to you. The person who sells GPL code has to provide the source code, but that doesn't allow you to resell it. Much in the same way you can have someone work on something for you in real life and give you the source for it, that doesn't however mean you can resell it without their consent.
They can however redistribute the GPL code, but seeing as they aren't pulling it out of the miner and are selling both SPs code and the GPL code it's still not legal.
One person breaking the law doesn't mean someone else can do it too, unless we're going by vigilante rules in which case GPL doesn't matter in the first place. Just another example of why nothing is enforced around here and why it doesn't matter.
If this isn't the case, give me a source for this, so far I haven't seen nor read that. What people are mistaking is in thinking that because something involves GPL code all the code then becomes GPL code. It doesn't work that way. The only thing they can legally resell is JUST the GPL code in the miner, assuming SP can prove he did the changes to the miner and that those changes from the code are his own, it's not legal to sell his miners.