The TechCrunch blog post and original graphic from Scores.org are both worth looking at since the text and comments do not mirror each other. What is fascinating is that Google has acquired SO much more than any of us realize, and this list is not complete. For example, it's acquistion of the Papers of Record is not shown. And it does not show partnerships, which is what has impacted Google's digitization efforts.
You'll wonder about the colors, etc., and what it all means. There is a key at the top. Blue seems to signify that the acquisition was integrated into Google's offerings. Note that some companies were acquired and left on their own.
By the way, someone has constructed a table showing the acquisitions of Google, Microsoft, Yahoo and Amazon, whom we might now want to call the 'big four'.
Research by Scores.org