I've just come across this article from Feb 2006 on the Google Security Blog called No More Deceptive Download Buttons. It was mentioned in a recent article on the Google Webmaster Central Blog.
It's a problem that I've been very frustrated about in recent years. This is Scrutiny's page on MacUpdate. This is an incredibly important page for me; Scrutiny is my flagship product and MU are probably the leading mac app site outside of Apple's Mac App Store (which I have real problems with and don't support).
My example here is from MacUpdate because of their importance to me, but the problem is everywhere, I'm sure you're more than familiar with it and are already skilled in hunting for the real link among the ads, or are blocking ads.
To be fair, the number of deceptive download buttons on that page does vary (There are more ads as you scroll down) and you get a different selection of ads every time you view the page (Google ads, via Doubleclick) but it's unusual for me not to see at least two big green download buttons high up that page.
It would be nice to see an end to this, but in these days of people expecting the product to be free, advertising comes into play, and advertisers will do what they can to attract that click.