No, it doesn't. A quantum computer would make very short work of a 512 bit key.
It does actually. Article and references both state quantum theory and relativity are the foundation in deriving the limit.
Sure, but the computation is classical, isn't it?
That is kind of misleading statement. What quantum computers change is not how many operations per second you could do, but how many operations you need to factor large numbers.
I believe that Bremermann's limit should also apply to quantum computers, but you are right in that example given for breaking cryptography is way off if you allow quantum computers.
We're veering off topic, but quantum computing algorithms extend beyond just Shor's algorithm.