Thinking about it now, it does make sense. They already have the largest ad network on the Internet. They have Google Analytics. They have Feedburner. An ad management application can fit well inside all that stuff.
Google Ad Manager will enable you to manage your advertising inventory, target specific visitors, produce reports and more. The interesting thing is that you can integrate banners that you will sell directly with AdSense units or even ads coming from other ad networks, and manage all that under a single interface.
OpenAds announced a hosted ad management solution some time ago, but now they will have some fierce competition. I like to host my ads on my own server, mainly because I am paranoid about load time performance. But now that big G is in the business I might give their service a try. They sure must have some big pipes to make sure that everything flows smoothly.
On a side note, what is left for Google to take?
Partner:
MakeUseOf.com Amazing Websites and Tools you Never Knew About