Yeah, but if someone reading your quote wants to verify that it's an accurate quote and not taking it out of context, they have to dig up the source article and find the text you're quoting. The blog post is also mutable, which means its contents may change after being quoted. Tweets are immutable and always have a reliable link, with built-in quoting functionality.

The one caveat is that a tweet or account can be deleted, but that's true for blogs as well so I don't view that as a mark against Twitter here.