I can understand those who offer reseller hosting services, they might use anonymous hostnames for their servers. Obviously the resellers themselves in general like private nameservers and anonymous hostnames.
What about good old single domain hosting (or multi addon), do you bother setting up your servers with anonymous hostnames or just opt for your main business domain as the hostname (with a nice name for the server)? I can`t see the point of an anonymous hostname for regular shared hosting accounts.
Anonymous nameservers are just as you said, mainly used by hosting companies that sell reseller/vps or dedicated server plans. Because their customers typically want to be hosts themselves... and don't want their "uplink provider" to be obvious... otherwise they think they'll lose potential customers to their provider.
I can't see any reason for offering anonymous DNS for shared hosting customers... except that it may be easier for the host to have only 1 naming convention for all their servers.
Also, many hosts will have both shared and reseller customers setup on the same servers, so they'll jus tmake the DNS names anonymous to cover the wishes of their reseller customers.