I thought "Droid" was one of the US carriers brands. I'd guess they're selling, and probably renaming, phones from various manufacturers to make them seem more coherent.
Motorola makes a phone called the Droid. However, they don't own the name Droid, Lucasfilm does (Motorola licensed it.)
If you look at pages for the Droid Incredible, you'll see they also licensed the name:
'DROID is a trademark of Lucasfilm Ltd. and its related companies. Used under license.'
My guess is that Motorola didn't get any sort of exclusivity from Lucasfilm, so other companies are free to call their phones Droid as well if they pay Lucasfilm for a license - and piggyback on Motorola's marketing spend.
Wikipedia says that the phone is called the Motorola Milestone in Europe, but called the Motorola Droid in the US because Verizon, who have exclusive US distribution rights on the phone, has licensed the name from Lucasfilm.
Actually, Verizon did. Which is why their top mobile lines (Eris, Incredible, initial Droid) are all called Droid, the Droid is called Milestone in Europe.
It's not confusing if you know that, in the US, the average person doesn't think about buying a Motorola or HTC. They are buying their phone from Verizon, so it's up to Verizon to market them. That's why Verizon licensed the "Droid" TM.
HTC wouldn't be able to come out with a Droid 2 because that's Verizon's decision. The Droid 2 is coming out later this year, made by Motorola because that's the way Verizon wants it.
If you look at pages for the Droid Incredible, you'll see they also licensed the name: 'DROID is a trademark of Lucasfilm Ltd. and its related companies. Used under license.'
My guess is that Motorola didn't get any sort of exclusivity from Lucasfilm, so other companies are free to call their phones Droid as well if they pay Lucasfilm for a license - and piggyback on Motorola's marketing spend.