The libraries maybe (and the runtime). The language, as per semantics and syntax, is more or less the same.
>Why not use C? Because C has no sensible packaging system, is unsafe, requires manual memory management, and offers a degree of control that is unnecessary for most tasks.
But is absolutely essential for most tasks C is used. For all the others, why not use a higher level language like Python?
>Why not use Java? Because it is verbose and picky and basically forces you to use an IDE to get anything done, etc etc.
Some people are not "forced": they choose to use an IDE, and wouldn't have it any other way. It is like telling some Smalltalk guy: "Smalltalk forces you to use the smalltalk image editor/environment" -- so what? He is perfectly fine with it. Heck, lots of people even like using dynamic languages with an IDE (and more would, if there was better type inference and assistance).
>If there were nothing wrong with these languages (they're the main ones we use at Google) we wouldn't have developed Go.
Well, the main reasons for Go, as stated in the official pages (the Golang FAQ), are not very convincing or exciting: No header files, faster compilation, parallelism, garbage collection, lighter type usage.