Sometimes that's just a byproduct of spending a lot of time with someone; you can't spend all those hours with a person without starting to see things at least a little the same way they do. Other times it's a condition they had to agree to in order to get that access in the first place.
You can't call this biography "slanted" without suggesting that Isaacson sold himself out. He may have, but that's a serious accusation.
And sure, it'd be nice to see his source material eventually. But I'd rather see the coherent package of his research in a narrative book form rather than his notes. I'll trust Isaacson to tell the story of Steve Jobs through his own interpretation, as that is all that a biography can be.
I'm not sure about characterizing a biography as a "commercial product"; although although it is the source of the author's livelihood, and the publisher is a for-profit entity, it is a complex entity as a product. The author depends in this livelihood in having access to materials from others, it is not unreasonable to think he may reciprocate in some circumstances. In any case, in future years (after the initial sales peak of the bio), releasing the source documents may even cause a revival of interest that helps residual sales.
It happens. Example: http://www.nytimes.com/2011/09/12/us/12jackie.html?pagewante...