In the past I've seen issues with Windows Updates because the CDN was 1 ms away. TCP wants to have 2 segments in flight, resulting in a non-responsive TCP stream below 13Mb/s. CDNs with low RTTs cause cause issues with low bandwidth connections. Not only does DSL tend to have a low first hop latency, it also tends to have less bandwidth than cable, making it a prime victim for on-site CDNs.
I just attempted to install a game(about 1GiB) from Steam and it quickly made about 20 connections to my ISP's on-site CDN. Even if you assume a 10ms ping for someone with DSL, that's a minimum of about 1.3Mb/s per TCP steam. Below that, TCP becomes unresponsive to congestion. 20 connections times 1.3Mb/s is 26Mb/s of packet flooding power.