I'm working in a company which got its own DNS servers, like many companies do. But I think they are not well configured. When I download files from popular CDNs like Akamai (read AppStore and Apple Developer Connection downloads) the bits are creeping through the pipe.
So I did a traceroute and found out the IP of the first DNS relay outside of the company network and used this one directly. Boom, the bandwidth skyrocketed to the expected level. So that's the reason why. But what I'm missing is what can the admins do to fix it.
I suppose it has something to do with reverse DNS lookup entries. But I'm just guessing. I should mention that we're behind a NAT for IPv4 traffic. And IPv6 isn't used for prime time yet.