As it's been stated repeatedly, the Air & iPad are two completely different animals. It's dependent on you specifically which one you need. For me, I have never been able to draw on my MacBook or Mini, without the aid of a tablet. The iPad makes that possible with absolutely no setup or preparation. Just tap Sketchbook pro & I am ready to go, wherever I am.
I've tried playing games on my MacBook or Mini, and with the exception of Solitaire or Plants Vs Zombies, I am just not the type of person that likes playing games on the computer. I didn't care for it much when I had gaming PCs, and still don't. I'm pretty much a gaming console fan, but the iPad does have that ease of play when I want to take a break and play something.
Ultimately it's the tablet OS that makes the difference. I like having just that screen to play around with, and nothing else in the way. True, when I have to write, I do go back to my MacBook, but in a pinch I've worked with the iPad. I'm not the sort that needs to do 'heavy computing' so the tablet / laptop difference skews differently for me. I like when I am curious about what is on tv, I can just pick up the iPad, hit the Yahoo entertainment app, and I have a great tv guide instantly.
It's all about your needs, one isn't really better than the other. Just better for some needs, over others.