I thought this has always been common knowledge... do people really think Xur only sold the gally in week 2 and every other week right up until there was a DLC about to be released they announced the gally would return with RoI... and all of a sudden it was in Xurs inventory again... They didnt let Xur sell the gally because it broke any mechanics they put int he game. They didnt nerf the gally because it was the carrot which kept everyone grinding away. They sold it again right before the release of RoI to get people to come back to the game and hopefully purchase the new DLC.