They've *never* allowed 2 banners on one page.
There was some confusing language in their TOS at one point that said you could, but then it also said you had to guarantee that they gave different advertisements, and since there was no way to do that, there was no way to run two banners on the same page. People saw the first part but missed the implications of the second part.
I think what happened is that they had plans to release some code that would allow you to specify that it was the second banner on the page and then it would force unique ads, and wrote the TOS to indicate it, and then it never happened, confusing everyone.
DNForum used to have two Google ads on their front page, thanks to a stealth ad in the Sedo news listing. That disappeared. Wonder if anyone official would be willing to say if that was because Google told them not to.
(come to think of it, stealth ads also are against TOS... wonder if they got a letter and, if so, what it said)