'Droid' is a Lucasfilm trademark, which Verizon licensed. On other carriers, Motorola and HTC handsets use different monikers.

Droid = Motorola Milestone

Droid 2 = Motorola Milestone 2

Droid Eris = HTC Hero

Droid Incredible = HTC Incredible

http://daringfireball.net/linked/2009/10/17/verizon-droid

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.