The difference between a website and blog is the amount of attention. Websites require time to create and have higher upkeep costs. Blogs are simple to start and cheap to run. A post on a blog can take 10 minutes - opposed to a new page/article on a website which will take (at least) 30 min to write, then pass it on to the webmaster, then publish, then make it visible....
In addition, websites need to look and sound professional in every sense. Blogs can be much more informal. Blogs try to 'chat' with potential customers while websites try to give sales pitches.