Simply put... The majority of what VZW sells is due to marketing. My sister was waiting for the Incredible but went with the DX simply due to the backorder, she doesn't understand the differences nor does she care. It's a nice device and she is happy but she also doesn't know better
And hence, we do know better but are simply in the minority to make a difference in sales. So it isn't bad marketing but rather a lack of marketing by Sprint (and other carriers). Since "Droid" was a VZW thing... It applies to all Android devices, whether it is HTC or MOTO. People come in and want Droid... That references 4 different devices. Brilliant.
I've seen Galaxy S commercials for Samsung, but they just want mind share so it hasn't been device specific. I could see them splitting costs with carriers for a specific device but they sell them to the carriers so they are already sold; we aren't the customer to Samsung, HTC, or MOTO (Apple is a different beast, can't use them to compare). If you notice HTC commercials are very generic and non-device specific.
Samsung really missed an oppurtunity by not creating a "DROIDDDDD" version of the GS for Verizon. Make it angular, mean, black, call it something evil sounding. They could have ridden on the coattails of all the android push that Verizon has been making over hte past year. Who the hell wants to buy something called the Fascinate?