The post for Stack Overflow en Español should not be in the community bulletin except on that site. That bug is getting fixed as I write.
As for other blog posts, including the excellent interview with Jenn Schiffer, there are no plans to change the community bulletin feed. For one thing, we occasionally use the blog to publish information specifically of interest to the network as a whole. For another, many sites that are not Stack Overflow are still geared toward the topics we include on the blog. Finally, even sites that are focused on less programmery topics still include many users who are nonetheless interested in the blog.
Advertising (and to be clear, using the sidebar for the blog is advertising) is a necessary evil. Our ad sales department doesn't run paid advertising on this site which leaves that space for community promotion ads. This could change in the future if we have clients interested in buying ads appropriate for Science Fiction and Fantasy. It doesn't make sense either for users or advertisers to run ads that don't pique the interest of readers of this site.
Stack Overflow blog posts in the sidebar remind me a little of spots promoting other shows on a TV network. While it can be a bit strange to see a serious news program being pitched between sitcom episodes, I recognize that some people truly are interested in both types of programming. Sometimes I've even seen ads for the parent company. NBC, owned by GE, is particularly strange with spots for power generators, jet engines and medical devices. While they sometimes fail to be ideally targeted, I do hope they entertain and amuse. And unlike GE ads, at least you know they will only stick around for a few days.