I googled broken aluminum frames as well and noticed that all of them were off-road bikes and I suppose we have to give them a learning curve. You had to be a little careful because some of those broken frames appeared to have been repaired via heliarc so it is unclear what actually happened.

The Redline cyclocross bike that had the headtube broken off hit pretty close to home since I have a version - the Conquest. Upon close inspection though it looks like a manufacturing error. The downtube broke at the weld and the toptube couldn't bear the stress. Remember that cyclocross bikes absorb all of the stresses of an MTB and are as light as a road bike. So you have to be ultra-careful with quality control.

And the steel bike failures did not appear to be catastrophic - bent downtubes from collisions with cars and the like. I am sure that there have been failures with steel frames that caused crashes and injuries but I haven't seen any and as you say, googling frame failures isn't a good source of information without full knowledge of the circumstances. I have seen pictures of broken chain stays, broken seat tubes at the bottom bracket and I personally had a seat stay break on a Peugeot el-cheapo producto. But all of these steel bike failures allowed careful return to home.

What we can say is that the drive for lighter and ever lighter carbon frames is putting a greater likelihood of catastrophic failure.