I was under the same misconception, which is why I was looking to change
my host record at NSI even though the domain is registered with OpenSRS
(and in desparation ended up posting to nanog).
Apparently it is now up to the registrar of the matching domain to manage
the host records, and luckily, OpenSRS does have an easy interface to it,
but I take it this varies greatly from registrar to registrar.