I've noticed that as well. That's actually what confuses me the most: If it really is a single, why can't I buy it anywhere? Honestly, I think that if people write it as a "single", they don't really care if it isn't available separately; simply calling something a single doesn't specify whether it's promo or not. For people trying to cater to consumers, like Billboard.com reviews, if it's a popular hit and/or music video, people know it; it doesn't matter under what technical details it was released. But I think the difference is that since we are able to specify this, we probably should. We should try to reflect the reality. I don't think having a music video and a high placement in charts does anything to change the type of single it is; I've seen music videos for promo singles many times before; even some for album tracks. Isn't it a promo single nevertheless if it's only available separate from the album for promotional purposes? It's not like this is degrading the single in any way either; some artists just don't release subsequent album singles separately for consumers because they'd rather prefer they buy the album.