Bungie is afraid if they state a price now (doesn't matter if it's $40 or $70), it'll scare off gamers as they compare against other shooters or Destiny. If they had confidence in their game, they'd state the price now just like how any new COD or BF games are known to the $70 early on and gamers dont care.
Stating the price only a month or two before launch is weird.
But what they are trying to do with the reveal and more content later is wow gamers so much that when they finally reveal the price, gamers are amped up and will pay it.