I clicked on the link in the second slide: http://golang.org
compare with:
http://www.haskell.org/haskellwiki/Haskell
Even Dart looks great: http://dartlang.org/
I feel a little guilty being negative about this, but presentation does matter, and Google ought to be able to afford it.
golang: small, simple description, download link, platforms, and UTF (editable!) hello world all far "above the fold" and following that nice "F" shape for where they put important information. very plain. very efficient.
ruby-lang looks like a web 2.0 CRM-built site. So much wasted space, so little obvious flow or prioritization of elements, even on the main page.
And the others attempt to describe things instead of demonstrating them, use a lot of vertical space for big images that don't inform you of anything, and generally hide the real meat a scroll away for what reason? They don't make a sale if I hit the big green button, but they do get a totally-uninformed poke at their system, generally leading to a crappy first experience.
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I'm not at all a fan of the slide show interface, but I certainly don't find it a bad thing that they aren't high on Photoshop fumes. Though they can sometimes be used to great effect, they aren't generally informationally dense, which programmers often prefer.
I like that the urls are consistent. To find package documentation, I go to golang.org/pkg/<name of import>. For example, for http docs, I go to golang.org/pkg/net/http.
For most languages, I resort to a Google search to find package docs. This is true for python, c++, and even Java. I rarely have to google search something in Go.
I think the site very much fits in with their goal of simple and orthogonal. I actually wish more language documentation followed suit and made it easier for programmers to search for docs.
Sure, everyone wants a pretty site, but it's not like they need to advertise anything. It gets the job done very efficiently.
That said I prefer the design of the Go website to all of those that you linked and that Git website still saddens me when I see it: I miss the old site :(
So, yes, presentation does matter but that doesn't always mean that it should be pretty. For some audiences, that can be a turn-off.
Reading this the average developer devices to continue using C++, which is all fun and games...