A problem how? If you want the money, and the blog is not disreputable, the only issue is that even when the rights revert the story will probably be discoverable online.
Of course, many electronic publications archive any story they publish. (Most will take something down if the author requests it after a certain length of time passes - 12-18 months seems to be pretty standard.) Since none of them are password protected Googlebots/thewaybackmachine etc always have a potential to have cached the work.
The question to consider with blog-pubs is - are they offering monetary compensation that is comparable to a more traditional publications (electronic or otherwise)? If the rights they ask for are similar, and the pay is similar, and they seem to be fairly reputable/have a decent readership there isn't much difference between someone publishing your story on their blog and publishing it on a seperate website. (If you really want to be published on paper, well, there's not any substitute for that.)
The Twitter fic publishers use dedicated websites, blogs and their own Twitter feed to publish work.
Where do you want to see your stories?