Risks? Sure, and so does the cloud.
As a back of an envelope, though, what's the chance that your residence will be burglarized or burn down? One in a 100,000? So the chance that both your house and the location of your secondary backup will burn down is one in 10 billion. That's a pretty good improvement for just the $100 it costs for a second external drive.
Anyway, yes, the backup situation is only the secondary plot here. From what I've read in this thread, this Gizmodo guy had *no* backup. For that, there is no excuse.
I could go through the reasons for the examples you mentioned but I'm sure you know them. The main difference between keeping it a location that isn't in a security box is that you don't have to pay the monthly fee.
Even then external hard drives are fickle especially when they are external in my experience unless you're willing to pay the premium.
I'm not saying that what you're arguing is incorrect but there are always scenarios where your data can be compromised.
You're also asking that each individual pay a large amount of money to keep multiple hard drives around while the warranty for these devices only last so long and they can't give you back the data you had which is more valuable than the hard drive itself. This is why iCloud or keeping a physical copy is still the best option for the masses.