The main problem with omitting the "Read More" call to action is that users will have to know that there is a full article and than the blurb they read isn't the full thing. On a blog format where a whole paragraph (or two or three!) is shown at a time it may be ambiguous as to whether that's really all there is to the story or if this is a blurb.
The New York Times does a pretty good job of making it clear that A) these are just blurbs and B) the article title is clickable:
NYT's blurbs are so short it's fairly clear there's more to the story, and the nice, blue headlines suggest that they are in fact links (they are) which helps guide users into clicking them to display the whole article. The "Read More" was likely a holdover of both an earlier web (where people might not have been expected to know how links work) and the actual print of newspapers, where front page blurbs often ended with "Full Story on Page X", copy that is no longer necessary. I suspect some times like the NYT might have ditched the Read More text simply because it did feel like a holdover from print.
It's important to note that sometimes the Read More text is more helpful, especially when a single page dynamically displays content via an accordion/carousel menu, such as CNN's Newspulse:
Read More is used as a call to action because clicking there actually expands the story, rather than taking you to another page. It's a nice little cue to how the system works which is good for a system more complicated than a page of normal links. You can click the titles here to "read more" as well though, increasing the clickable area.