What if Undertale or Her Story were $60?
I'm not disagreeing with you, by the way.
I don't think every game should cost the same. Those examples are short, focused experiences. No Mans Sky looks more like a traditional, lengthy "AAA experience" based on the advertising and marketing narrative so far.
The idea that an ambitiously massive game should be heavily discounted just because it's from an indie team is flawed. No Mans Sky could end up being a steaming pile of shit but until then, if we believe the marketing hype, it looks worthy of a full price.
Basically it comes down to this: If Nintendo was making this game nobody would question the price.
(Etta, I answered your question in the first paragraph and then kinda ranted. It wasn't directed at you...)