All top level domain registrars are issued directly by ICANN (The Internet Corporation for Assigned Names and Numbers). that approves they're qualifying toplevel domain registrar instead reseller etc..
Think it like the central government of the domain world. That is the way I see it at least
By the way, it is one of the questions on HE.Net's IPV6 certification test, so make sure you get the answer right if you want to take that one
ICANN coordinates domain name registrars which in the most cases do not provide web hosting.
If you see web hosting company offer domain name registeration 99% that is being offered as resellers. Most web hosting companies deal with registrars not with ICANN.