Hmmm blogs and forums are two completely different things and hardly ever look the same.
Blogs and forums are the same in that they list recent topics or posts in chronological order and have different categories in which posts or threads go in to.
But a blog is more of just a platform to publish content on, articles etc etc. Example WordPress, Blogger, Tumblr etc.
Where as a forum is a platform where discussions can take place and you have your own account/profile and features that come with it like private messaging, avatar, signature etc.
Of course, discussion can take place on a blog in the comments section for those blogs that have comments/commenting enabled.
But with a blog, it's not the same as a forum because with a forum you get your own profile, post count, forum abilities, private messaging etc.
Forums are for communities, a place where people can come together and discuss things together.
But a blog not really for a community, its just for writing, publishing articles, posts etc.
Some forums, such a this one, provide a blog as well though. Example
http://www.webmastersun.com/blog.php
Neither are more advantageous than the other, both have their own advantages and disadvantages.
Blogs generally let you post more content and you can post what you like if it's your own blog.
Some blogs are very SEO friendly and have features that search engines like such as RSS feed, Sitemap etc.
But then, these days you can get all of that with a good forum platform such as VBulletin etc anyway.
Hope this helps!