A domain that isn't fragile enough that one company can take it down. Systems like namecoin or ens don't suffer from this problem because they are actually decentralized.
You have to host somewhere ... and that is usually owned by, you guessed it, one company. There's always a single point of failure, whether it is your power company, yourself (you will die one day, or get injured, or sick)... there are so many failure modes.
It is infinitely more likely wherever you are hosting your domain to shut you down vs. DNS.
