If availability is a security concern, than yes DoS is a security concern, but only in so far as all other bugs that limit availability are too. It is not a security concern per se, regardless of whether availability is a security concern. We don't treat every bug as a security issue.
The linux kernel does the opposite, they do not believe in security vulnerabilities. That's why if you mention "security" in a patch, Linus will reject it.
Well, the Linux Kernel project actually does.