You'd be surprised how many HD radios are out there now due to iBiquity's aggressive push to get it in new cars. I'm seeing the logo on at least half the radios in new cars I'm seeing out there. Whether or not it's turned on and active is anyone's guess, but considering how poorly the HD is maintained in most markets, I can't imagine it stays on for long in the hands of purchaser.
A translator like this would do good to occasionally mention the HD broadcast, since WDXB's HD coverage, at least when sitting still, is much, much bigger than the translator can cover. The few times I've visited Birmingham in the past, I've stayed in hotels on the outskirts of town and have had to resort to the HD feeds to hear any of these formats. None of the translators have enough punch to really penetrate hotels, which are full of noise.