it's hard to be frank and honest without having investor confidence and stock prices drop. That's truly who the audience of the letter was.
Do you remember how Wall Street pundits jumped when Larry Page did some frank thinking? Nothing happened. They went on and silently released Google+ this week - its interesting to see market react to all this.
Market analysts want to hype up the stocks. And any amount of introspection on the company's sides negates their efforts. Thats why they are pissed when somebody stops shoveling the crap.
But markets themselves don't really care - if a company does good - it WILL reflect on its stock price.