They don't need to close the source, just figure out some way to indicate to buyers that if they buy an Android phone, they're guaranteed to have a certain experience.
I, for one, don't see the proliferation of Motoblur/SamsungSense/HTC-Whatever to be a negative thing. It is an additional factor that consumers can use to differentiate between phones. One reason I own a DroidX is the great hardware, but another reason is I think the moto skin adds a lot in certain areas (it's calendar widget, for example).
In other words: let the market decide.
Having said that, I have several family members with HTC, "Sensified" Droid Incredibles, and it doesn't seem to be that bad. (Then again, there is no NASCAR app either...)
EDIT: Some clarification and grammatical fixes.