While I don't entirely disagree with your point about the "open internet" being another kind of walled garden, there are definitely companies and organisations that have taken steps to ensure that the open web is actually "open," and Google is one of them. Evidence: https://www.google.com/takeout, which lets you export data from almost all of your Google services.
Some major innovations from Android have inspired sister projects for the open web, like http://webintents.org/
Also, I think you're misinterpreting the term "open internet" ; it usually means "open" for the developer, not the user. However, it's still better for users, as competition between open standards and technologies means that they usually get the best solutions (exceptions being things like h.264) This is certainly better than the classic walled garden where one company gets to decide what developers may or may not use.
In short, it's better because it's: - unfiltered (mature content, etc.) - unrestricted in terms of technologies used - partially open for users
takeout is not the same as interoperability. Google's new products have very weak interoperability (APIs to non-Google clients)
I don't know why people keep complaining that Google+ doesn't have an API https://developers.google.com/+/api/
It is readonly.
The 'open internet' is often just a reverse walled garden. Things used to be locked down on your device, now they are locked down on remote servers where you couldn't even pry them out if you tried hard & ignored the law. (Unless you're the US government, in that case things have gotten much easier.)
The only advantage is that there is no middle-man between you and using any app (website) you want. But no company has ever tried to restrict web access on its devices, so where's the advantage?
And judging Google by its products: Google+ actually seems a lot more closed to me than Facebook (hardly any API?). Android itself is open source, but it is hardly about pushing the open web either. (At least it stopped pushing Flash)