It's a verb phrase because it's a call to action; in your blog example it's also navigation, but it's not the same as labeling a link "click here to go to X". Users already know how links work and they want to know where the link goes or in this occasion what a link does.
Calls to action are usually buttons because of the visual differentiation and emphasis that buttons can give, as Smashing Magazine describes. However a link on a website can serve the purpose of simple navigation (in which case the action is obvious) or actions (in which case text or other context should tell you what the link is doing).
Take a look at our FAQ, the "show more" links are more clearly calls to action and the act more like actions than navigation, but functionally they're similar to a blog's "read more" links, a blog could even use javascript to immediately show the whole blog post when clicking "read more" making it more clearly a call to action rather than navigation.
More about link text and calls to action.