It is of course true that the author should have deployed to two zones. That said you'd still noticed something is going wrong and now need to identify what's happening and if you need to take any corrective action. Being easily able to see that half your infrastructure is down and you didn't break it would save allot of time and nerves in a potentially critical situation. Unless you significantly overprovision you likely will also need to scale up the other zone. For that decision making it's again important to quickly know what's happening. Amazon's reporting helps nobody but their reporting and probably internal metrics and likely bonuses.