I believe this song to be about the superficiality of love. Bono appears to be singing as though he is lamenting over all the conditions etc that his love is putting on their relationship. She is asking for all these material items, and promising how great it will make their love. This means nothing to him though. In the end, all promises will eventually be broken and meaningless. Bono doesn't feel any of these promises are necessary. He doesn't care for the little superficial things she wants or is offering, because really all he wants is her - not the promises, not the material items - just her.
This may relate in some way to his wife Ali, because I believe at one stage they were having many problems, which may have been related to demands by her on their relationship. Bono may have been writing as a way of expressing that while they were having problems, he still loved her beyond all of that. However, all of this may very well be false.
I would guess the basic meaning is about how Bono wished that whatever relationship he is refering to was a lot simpler and could just be, instead of having conditions put on it.
Ted Beak tedbartholomew.com.au (28:th of November 1998)
"A lot of videos seek to explain the songs; whereas, this is more of a parallel to the song. We're using the story ... of Gianni, the circus dwarf, and Rossa, the beautiful trapeze artist, as a way of explaining the theme of the song." -Bono in the video clip from U2.com, Rare footage from the making of the "All I Want Is You" video.
From Salvation in the Blues, compiled by Chris Taguchi christaguchi.ca (3rd of April 2007)