I was pretty sure that auto-downloads were enabled by default. If not, it seems like most people have them enabled.
I don't think so, though I could be wrong. I actually prefer to have that option on on my devices (and my wife's) because we don't often buy things from iTunes (and when we do, it is often for a "want it right now" reason). I remember turning it on manually.
Most of the screenshots I saw full of rage on that site, twitter, and elsewhere showed the cloud download icon (with an accompanying "omg! this is using up my space on my phone!" missive). This leads me to believe it is more likely that people don't understand how it works.
Full disclosure: U2 is one of my favorite bands. I don't know if they've put much out worth anything since Zooropa (which was, itself, mediocre), but their old stuff is among my favorites (The Unforgettable Fire is still a brilliant album).
However, even if they put something on my device that I despised (some modern country album, for example)... I don't think I could get my dander up too much. I mean, it is free. Who cares if you happen to not like it? Delete from my device(s), delete from MC (which would have grabbed the download), ignore in iCloud, done.