I agree, to a point.
Senior exec's don't have enough time to dig through a detailed post and reply chain to find the information that is critical to their work. The more fundamental issue l;es with middle managers' ability to communicate effectively up the line. In other words, if you want an executive to read your blog, make it worth reading. I hope I'm not violating that rule with this blog! If the wiki contains important data, presented in a way that facilitates executive decision-making, then the senior leaders will come back to it.
But let's not get to too disappointed if it takes 5 or 6 more years before these become commonly accepted work tools. We would be well-served to remember that all of these tools compete with email for attention. And it seems that email is still winning.