This is my opinion, I think utada, idj, and her management did the tour in order to have another "taste" of her american fanbase... kind of to see if we'd still respond after her long absence due to her illness which postponed her appearances and probably anything that could have come after that.

I think DD was released for that purpose, for the tour.. so the tour wouldn't seem completely random, in other words the tour was not really made to promote the single but only made to look like it was. Did the tour really promote the single? I honestly don't think it did, but that's my opinion. The tour sold out without promotion, and i don't think DD has had airplay in major radio stations either...

now for what comes after the tour,

The tour has ended, and by the last message utada posted... it seems as if she's going to rest for a bit... (in the mean time i think IDJ will decide on what they want to do next). utada did her part in showing idj that she does have a fanbase and that whatever happens next she will have some support...

after she got sick, I really think that utada was very insecure and unsure of what she wanted to do. I think that not only her but also IDJ thought that the prime time for her to promote the album, which was after its release had long passed. BUT before completely giving up on the album i think they wanted to have another round, to see if they could "revive" it, thus the tour.

the result is obviously positive, and now IDJ will either push to promote DD more or release another single with a lot more promotion than the previous singles... or both. I also think that this time around Utada will be more enthusiastic about promoting TITO.

In the flesh left a very good aftertaste

EDIT

I also think that her next rumored song/single "Show Me Love" isn't showing in the Goetz B. Profile, because Utada probably wants to continue promoting just a bit more for TITO before going back to Japan. I think she realizes that she probably won't be able to jugle promoting back and foward between Japan and the US.

but all of this is my opinion and predictions