The "Community Promotion Ads" were actually born out of the "Open Source" initiative Started on Stack Overflow. So Stack Overflow had the community-driven ads first. 

It was the early success and overall good will of the Open Source project that made us thing that, perhaps, *other* communities would appreciate having this feature, too. So the two programs are essentially one in the same, except that the other sites don't have the same sense-of-purpose for those ads as Stack Overflow (I wish they ***did,*** actually… but we're not there, yet).

**So why doesn't Stack Overflow just add the general Community Promotion Ads to the mix?**

The Open Source advertising initiative is such a successful program. We have allocated, essentially, a block of "free" advertising to this program. I'd hate to lose that focus by opening that space up to a bunch of *other* things people might like to advertise. I can appreciate that you want to promote other sites and a plethora of other things here. But there are so many open source project needing our help. I'd hate to lose that focus by diluting that space with other promotions.