Why not using nameservers on Domain mapping?

I've been reading on document for Domain Mapping plugin and I only see that "CName" or "A record" are the only way to have a domain pointing to a subdomain.domain.com on Wordpress Multisite.

My quesiton is why not using Nameserver like ns1.domain.com and ns2.domain.com? I am running this Wordpress multisite on a dedicated server with dedicated IPs and I am able to provide ns1.domain.com and ns2.domain.com to any domains that wants to point to my server.

So why not nameservers as a method of pointing domain like this http://en.support.wordpress.com/domains/map-existing-domain/