Dancing Barefoot and all the other covers that U2 has done are not on the digital box set, either because they didn't want it that way, or they couldn't due to not owning the copyrights of those songs.
They would've had to pay royalties to those artists, which equals less money for U2.......and they would've had to negotiate the rights with those artists, which I don't think they had enough time to do if they wanted to release the boxed set on the same day as HTDAAB........
Funny, I'd never really listened to Dancing Barefoot, and then the film THREESOME was on the telly the other night, and I suddenly noticed it's part of it's soundtrack.