Take a look at the measurements on both sites again. Seeing how both tanks were made in cm, when converted to inches, one of the sites rounded up. According to their measurements in cm, they are the same tanks.
You're right. GLA rounds 14.17in to 15, and 10.24in to 11. Maybe GLA was including the glass in their measurement or something... If they did, then they may have also rounded 5.5g to 6.