I bring my Air to and from work every day; at work I have a power strip under my desk, and it's easier to access from the front (and also less of a hassle to unplug and replug every evening and morning). At home I have a power strip under the front of my couch; when I have the laptop on my lap on the couch the cord goes out the back, but if I place the laptop on my coffee table, the cord comes back to the front.

Do I represent a common use case? Dunno...

You're right, I generalized: the position of the power outlet varies with every place you plug in your laptop. However, I often find myself with the outlet behind me (i.e. sitting against the wall at an airport, restaurants; I take my laptop out of the house with me frequently), so I run into this problem. I liked the perpendicular adapter because in the worst case, the cord had to make a 90 degree turn.