I've said it before, but I have always been under the impression that, if he could have, Sean Murray and Hello Games would have delayed No Man's Sky until 2017, if not longer. I think the team had every intention of including the things seen in early trailers, and talked about in interviews in the finished product. Unfortunately, business contracts don't always allow for that type of creative expression. It was one thing when Hello Games was working on this project in their own indie studio bubble. Once they signed whatever deal they signed with Sony, I imagine a great deal of that freedom was reduced. They were no longer able to take as much time as needed to implement every feature they wanted to implement.
I think the delay to August was a courtesy. It was a "get this thing done because we're trying to make money this summer" sort of courtesy. For better or worse, Hello Games had to ship the game no matter what. I believe they tried to create as complete a game as they could, with as many of the features that were functioning at, or close enough to 100% to not completely disappoint.
I bet a lot of the missing content will be added over time. That's unfortunate that it couldn't all be there day one. But it's also the reality of the industry. No one is more disappointed by the inner politics of game development than the developers themselves. There isn't one out there that doesn't want to release a game that they can be proud of, and that the intended audience loves. Most of us create the things we'd like to see/play/read, etc, etc, so when we fall short, for whatever reason, it sucks.