I would assume that the FCC expects that, someday, HD will have an audience.
Though I agree, the jury's still out on it, HD at this stage is where FM was in 1965 or so. Those station also did Conerad, er...EBS...er, whatever it was called then, tests. So, I can agree with the FCC ruling requiring
EAS on HD-2 channels.
Don't forget, EAS is also required on those cable channels that you swear have to have, oh, about 20 people watching up on channel 698, or so. (channel number varies according your cable service.)