There is more to platforms than operating systems. I worked on an application that had to function on 8 different hardware architectures[0], though on all but one we ran Linux. We also had code that was bare metal (no OS) running on FPGAs and DSPs. Go is a long way from supporting that.

This is not to say Go will not get there eventually, if the language gains popularity. Someone had to write or modify a compiler to target all those architectures for C, after all. This is just a reaction to what I see as assumptions tying operating systems to certain hardware architectures (in this and other discussions). Go can be used on a range of operating systems on two hardware architectures. Very good progress, but the language needs to get that second number up before we can seriously talk about it replacing C.

[0] Only had to perform well on two, fortunately.

+ FreeBSD.

Also, OpenBSD, NetBSD, and Plan 9 in the works.