Probably not common, but for me, the appeal (and it is VERY appealing) is vastly more aesthetic than physical, which means that small(er)-breasted women are strongly encouraged to apply.
Technically, it's not a titty-fuck if she HJ's you to a finish on the girls, but apparently it's fun for her to watch your reactions/release-face. And anything that involves cum and tits is high on my list!