Except that's obviously not the case, considering he just announced Negroni, an idiomatic ("non-magical") library that provides the key feature of Martini.
...which has even less features than Martini.
Because it doesn't need them. There are more polished versions of those features elsewhere, and they can be composed easily with Negroni as they all use the same interfaces.
I thought your point was about the necessity of magic in a web framework. The most magical thing about Martini was its dependency injection approach, which Negroni provides in an idiomatic way.
Unless you're saying that it's the magic that makes a framework a framework, as opposed to just a collection of libraries. That makes sense, because the magical approach of Martini (for example) does, in a sense, lock you in to using Martini. This makes it more like the monolithic web frameworks you mention.
The reality is, when your language is as weak as Go (in terms of advanced features), a framework with any sort of significant features will be quite dynamic and "magic".