Also - the name Coke for Coca Cola was adopted by Coca Cola after people started it calling it that for short.
I can understand calling any Cola drink a Coke just for brevity or whatever but...Saying 'Coke' for a Dr.Pepper, a 7Up, a Gatorade, A Mountain Dew...nah.
EDIT : Although... I guess since Coca Cola the Company probably owns a lot of those drinks - I guess it *kinda* makes sense ?