But what if you put a proxy in front of your proxy?
Or additionally created a DNS round-robin for several?
Or what if you had 9 firewalls?
Or.... or... or...
Also, single point of failure is directly related to what you're trying to prevent....
Clearly, using your own proxy is not a single point of failure in relation to DDoS against Deepbit. It's actually a robust system in comparison to one-miner-one-pool.
If your proxy is being DDoSed offline.... you have other issues.
Speculating about the faults of a system by using faults of other unrelated systems is silly.