Couldn't disagree more. Many of us (myself included) use our MBA 11's daily for real work. In fact, when I bought my 11" I bought it for exactly all the reasons you listed under your reasons to buy a 13." I've been using it daily for 6 months now for work and graduate school and it really is quite the machine. Now I agree that there is no "right" machine to buy, (to each his own), but the 11" is indeed very capable and is, to many users, much more than what you described it to be. It's a little silly to spend so much money on this type of computer for the reasons you listed. Honestly, if I needed something to use for no more than an hour at a time I would just go buy an iPod touch.
I have both and, in my opinion, the two are miles apart. The only thing they really have in common is their relative size. I love my iPad but could not use it alone for school. Yet, the MBA is perfect for me as I need it for mostly writing and I am not bothered by a lack of vertical pixels. I've actually found that the two complement each other nicely. It's great to be able to have a book open on the iPad while i have my notes in Pages open fullscreen on the MBA. But again, to each his own - what works for one person won't work for everyone!