I think, ultimately, it relates to how you approach code. Coding on the iPad is a kind of relaxation/holiday thing for me, but coding on the MBA is more of a working-at-my-desk thing.
That probably doesn't make much sense to other people, but there's a fair few that agree, e.g. http://yieldthought.com/post/31857050698/ipad-linode-1-year-...
The largest projects I have worked on are an order of magnitude smaller and even for this size I am unable to imagine how you could replace working on a solution with 50 projects in Visual Studio with just using Vim.
Not to mention coordinating 10, 20 or 50 developers if everybody is sitting under different trees. At least for me given my experience in developing software this makes absolutely no sense.
danbruc - there are instances where an iPad is more convenient than a laptop. Also, this is more than just a text editor for the iPad. The cloud development part plays an important role.
I think what you meant to say was "but I'm not productive this way." Clearly many developers are more than productive without a big screen/multiple screens, mice, and external keyboards. And as someone who has been shipping for several years with nothing but a 13" screen, I'm definitely one of them.
In fact I'd argue the ability for me to be totally mobile and work from wherever I want, whenever I want, makes me _more_ productive than being tethered to a monolithic workstation. There's a lot more "oh hey, that code I wrote last night kinda sucks, let me fix it before I hop in the shower" and a lot less "oh I should probably get around to fixing that thing when I get to my workstation."
Good developers write apps to scratch their own itches, and this seems to be a laudable example, whether it scratches your itch or not.