I don't think any one even has MBA as the only computer. It doesn't have firewire, only one USB and no built in DVD/R/RW drive. But as I recall, it was also specifically introduced as a second computer, assuming you already have another beast running OS X (or god forbid, something else). I don't feel a compelling reason to run the full fledged OS X in every device. That is why why feel that one light weight companion device can be replaced with another lightweight companion device for many, but not all, users.
Therefore I do feel that low end MBA would face at least as much competition from iPad as the top end iPod touch.
Therefore I do feel that low end MBA would face at least as much competition from iPad as the top end iPod touch.