It is, but one of the virtues of the Go ecosystem is that it's also often very easy to fork the standard library; people do it with the whole TLS stack all the time.

The tension Ted is raising at the end of the article --- either this is an illustration of how useful casting is, or a showcase of design slipups in the standard library --- well, :why-not-both:. Go is very careful about both the stability of its standard library and the coherency of its interfaces (no popen, popen2, subprocess). Something has to be traded off to get that; this is one of the things. OK!