TLDR: The Go team got some (dubious?) legal advice [1] that the site violates certain OSS licenses, so plans to close godoc.org and bring up a more limited service at [2].
[1] https://groups.google.com/forum/#!topic/golang-dev/mfiPCtJ1B...
[1] https://groups.google.com/forum/#!topic/golang-dev/mfiPCtJ1B...
That presumably means that other lawyers who have considered such services have not drawn the same conclusions.