I guess the other point is the matter of trust. Iwata speaks on very specific terms, and measurable ones at that. Either he is lying and the games/hardware never come out, or they do. Given that most of what Nintendo have announced in the past few years have released within a year of announcement, it has been easy to evaluate whether he is honest or not.
You can't say that about game journalists, partly because of questions as to who is manipulating the information - the publishers, the editors, or the writer?
Further, Iwata has apologised for things when they have gone wrong. I can't remember the last time I saw a game journalist apologising for product placement or inaccurate reporting on multiplatform performance issues.
The expectations are different - from games journalists you expect editorialising, are suspicious of motives and influence. With Iwata, you know from day one he wants you to buy his stuff, he tells you what they are selling, how you can buy it and when.