Well... as you know, japanese usually don't pronounce the L sound. I mean, in fact, it doesn't exist in Hiragana. However... as japan is being very influenced by the american and western culture in general they often prounounce the R as L [in songs] (generally)... I don't know why.. maybe they think it's softier or prettier. As for the G and N/M, my japanese teacher (who is, in fact, japanese) said that it's more polite to speak the G sound softly, making it similar to an N sound (but not that, exactly). She also said many people can't do that sound anymore, or just don't (it's very "traditional"). That's it!