Many people don't know there's a difference between the two, and Verizon has so well marketed the Droid name that many people have just started to call any Android phone a Droid — kind of like people calling any tissue Kleenex.
Notice I said Verizon has marketed this — even though Motorola was the first manufacturer for the Droid, Verizon has the Droid naming rights — hence the HTC-made Droid Incredible and Droid Eris.