The Asus Slider is the same thing as well, touchscreen with a keyboard underneath in a package a bit bigger than an iPad.
Remember that a Macbook Air isn't officially upgradeable by yourself, you'd certainly need some technical knowledge to do it.
Personally, I've got both a Macbook Air and an iPad and they do different things. If you want something for work, then the Macbook is a far better bet as it obviously has a proper keyboard and a mouse, but I think the iPad is better as a media player and interent browser simply because of its convienience