@ragingloli many deities throughout history have been specifically referred to as GOD, not just this upstart Jehovah. The Christian/Jewish GOD is barely 6,000 years old, there are numerous GODS, in fact, thousands, that, when they were in style among their followers were most likely referred to as simplyGOD. No ‘a’ needed, or even a proper name. Certain Christian groups refer to this diety as G-D, so how do you know they are worshipping the GOD on my money? There are four other vowels, you know. Maybe they worship GAD, GID, GED or GUD.
Face it, Christians are just lazy, they assume that when they say GOD everyone knows exactly who they are talking about. History says that there are approximately 2,500 known GODS in our recorded history. There are about 27 with the exact same storyline and myth as Jesus, all the way down to having a mother named Mary, performing miracles, being persecuted, dead for three days, ascended to heaven, etc, etc, etc, and most of them existed thousand of years before Christ, and were worshipped by lots of followers for a very long time. There is nothing original about Christianity at all. More of the same, cobbled together from various other belief systems.
But back to your point, sure Christians refer to other GODS by name, but the followers of those GODS most likely called their deity GOD, so your point is actually erroneous. Learn some history, the truth will set you free. :-)