I don't like being the bearer of bad news but this magazine is NOT the only print magazine licensed under the GSL that prints 4ematerial as they claim. Dragon Roots print and pdf magazine is licensed under GSL and the OGL and prints both 3.5 and 4e material and is at least 70 pages high quality print. Also, I am sure that Kobold Quarterly also contains 4e material. You can find out more information about Dragon Roots magazine at DRAGON ROOTS.
As the GSL currently stands, you cannot publish the same "product line" under both the GSL and OGL (and I think it would be hard to argue that two articles in the same magazine are different product lines).
Kobold quarterly has published 4e material, but it does not use the GSL. I know it's a fine point, but it would make the statements at Ogre Cave (which may or may not be Goodman's) technically correct.