Registrars and name servers

[Thomas Duterme]

Hi All,

My registrar is register.com.  When I first registered my domain
(madeforchina.com), I made two nameservers for the domain:
beast.madeforchina.com and grendel.madeforchina.com.  My domain now only
has one name server acting as authoritative: grendel.madeforchina.com.
When I first defined these two name servers @ register.com, they required
me to give an IP address for each name.  Now, each time I need to change
this domain's IP, I still need to go through register.com to make the
change, even though these are third level domains.  My main question: why
does register.com have authority over the association of an A record with
this third level domain?   

I guess I am a little confused between the relationship my registrar plays
with my domain and the root servers.  Why does my registrar control the
associations of my name servers with my domain?    Do I have to go through
my registrar to associate and advertise a new nameserver to the internet?
 
thanks,
Thomas