I think Bryan Coverdale on cricinfo summed up pretty well why Smith probably was not included:
Yep he's pretty on point. Just found it interesting that they've deliberately ignored Smith who did well vs spin for another opening batsman in Rogers. Not saying it's 'wrong' (Smith was hardly Bradman...) but the Aussies are clearly laying their cards on the table about the type of player they want. And that England could easily exploit that with home advantage and using Graeme Swann early and often against the left handers. That and only choosing one spinner and it looks like the Aussies aren't expecting a lot of dustbowls Not a very flexible squad would be one way to put it.
You could be right about the later Tests being the ones for the spinners. By that time Fawad Ahmed will probably be in the squad as the 2nd spinner, and we'll know how the team of openers is doing. Reinforcements can always be called up. Bailey is doing the right thing by being over there for the summer.