It's not right. Check out the GS trade thread. The last reported values for it were $10(12/5/11) and $7(12/21/11).
So me thinks someone got their wires crossed somewhere cuz GS values rarely go up and if they do they wouldn't go up THAT much.
I think he just poorly worded his sentence.
He said he's trading in two copies of Batman. So, I assume he's also planning to trade two copies of Rage. If Rage trades for $10 base, +30% for ME3 preorder and +10% for PuR, that's $14 a copy. Two copies, times $14 each, equals $28.
I could be way off, but that's how I'm reading it. Honestly doesn't seem that great to me. Assuming best case scenerio (for most people) is you're already a sub'd member of @GAMER, that means you have one coupon, and would need to buy one more magazine for $6. So, you're spending $6 + $5 + $5, for a total of $16 + tax. To get $28 back. Eh, I guess that's $12. But factor in time and gas... meh. Maybe that's worth it for some. Who am I to judge?