Actually it can make a noticeable difference if casted at the correct moment. I certainly notice a difference between playing with people I know who do use their role actions, and pugs who do not. Even if the tank is the same player and the content is the same.
I never made any claim they were on the same level as a healer. I did however say that they can help a healer to contribute more dps if said abilities mean healers have less to heal. Palisade is sometimes the difference between me having time to do three more dps gcds and having to choose to heal the tank instead. That's just one ability at one time. All those gcds add up over time in content. I can easily miss out on 20+ gcds of dps in a dungeon because people forget about their support abilities.
And seriously these abilities are one click buttons. That's it. It's not difficult to do so why not do it? If you're not weaving in an offensive ogcd what's wrong with weaving in a support one? Oh right. I forgot. It's this thing called effort.