[@Double] The history of the Kamehameha is well documented, the history of the Galik Gun is not. Hell, as far as i remember, he's only actually used it twice. After looking it up, i was incorrect, over the course of Z, he used the move a grand total of 3 times (Fun fact, this means that, in Super, Future Trunks used the move more than his father did in Z, using it 4 times) His move of choice was always Final Flash or Final Burst Cannon. So, don't treat the move as if it has some epicly important implications. It is stated during the first fight between Goku and Vegeta that the move is very similar to Kamehameha, so it would make sense that the Galick Gun was invented by someone familiar with the Kamehameha.

Also, i'm essentially answering the question of "What if the saiyans had kidnapped Roshi and made him train them in his form of combat?" There's no goddess worship, more like the respect that everyone gives to Roshi. Hell, even after Krillen far surpassed him in Z, he chose to train with Roshi when getting ready for the Androids.