not sensible at all
your confusing the website of a small business or one that makes no money with Alexa's top 1,000
while their maybe some outliers all of those will be making money from their website/presence
This is not about having multiple or even backup DNS run by a specialist it's about your root
its a bit like drawing an analogy with the military (Completely different sphere). However to respond to that Its like allowing your nuclear arsenal to be guarded, deployed and armed by a third party....
Biting the hand that feeds IT
