My theory is that they hope everyone uses their "Open" Chart API, which doesn't include the full service's abilities, so that their own charts, using the entire breadth of charting power, are inherently better than yours. Beware the wickedness of the corporate greed, my friend.
My sarcasm drips onto the floor. Now, I mean no disrespect to Marty, but this kind of post really does get under my skin from time to time. Maybe it just struck me at the wrong time. So what if Google has features they didn't document? So what if they use a different URL to access the API? Maybe the undocumented features are still in flux. Maybe they like to see how many people outside Google are using the charts. There are plenty of good reasons for everything he talks about them doing with this and claims it to have some anti-open nature, but I just don't see any of it.
For Google's Motivations This Means...
None of it really matters, in the end. Use the API or don't, but I don't see a gain for them in the parts of the API they are letting us use, nor do I care if they do gain. Gaining from something doesn't negate your ability to do it for the reasons outside your gain. My job involves writing software for a company that helps low-income families find affordable housing. I get paid for my job, so does that mean I can't lay claim to any good nature behind it?