There have been arguments about this for months, but Google has finally made it clear — you are allowed to show ads from more than one AdSense account on a single page.
For revenue-sharing sites, it makes configuration much easier. Instead of having to make sure all of the ads on a page are from the same account, you can mix-and-match however you want. This has been the case since the last TOS revision back in February, but there has been a lot of confusion. Google simply wanted to make it clear.