I should think the second example was more explanatory.
It is not necessary to use the directory name /blog for a blog. A blog will be found regardless of the directory, though it is a clear directory name, I would not use it.
From an SEO perspective, and if it were my site, I would have a /releases directory with a list of releases that links to the blog entries if that is where the releases lie. That way, you are getting the full potential of the keyword release. Or perhaps press release, news, what's new, etc. It all depends upon how many releases you may want to execute. If only a few, then the release page could be seen as being less fresh. But if you send say one a month or every few weeks, then it may be of value.
From a marketing perspective, depending upon the blog software, it may be better that press releases where clean - devoid of any other web engagement mechanisms. This is because the press release world rotates on a slightly different axis. It depends on how formal your press releases are. For example, are you notifying the press by releasing a formal press release? If not, then the releases directory and page with links to the blog should perhaps be fine. Otherwise, I might think that using /blog for releases would water down the effect of having releases.
I used to live in a world where marketing rapidly developing bleeding-edge technologies required rapid press releases (several a week) to magazines, news outlets, niche publications, various trade shows, etc. Having formal press releases and releases as an online presence that was clean was required so that these releases could be used in publications and news outlets we had not notified. In that world, press releases were more formal and followed a formula and tradition in an open way. However, if you are more casual in your releases and do not require formal releases, then a blog will be more than fine. If your releases are more newsletter or e-mail marketing in nature, then a blog is perfect. I guess it all depends on how many releases you actually send as to whether a /releases directory is wise. Just a few? Don't bother. One or two or three a month? Then I would create a /releases page. Informal? Go ahead and use your blog software. Formal, then it may require a different template.
Clear as mud?