What defines a Blog today?
Is it that it is published everyday? Is it that it runs on a "blog" engine like WordPress? I would say no, and no. I have a few sites that automatically publish information, not everyday but every hour; I don't consider them blogs. And also no to the second question, The best example I can give you is the company I work for. We have a website that runs on WordPress, yet it isn't a blog.
Here is my idea for a definition of a blog, A website or webpage with substance, and regularly updated content, that is easily accessible and shareable via standard technologies. It should provide a way for visitors to give feedback. It should also be accessible via all major browsers, conform to accessibility standards, and brownie points if it interacts with third party applications, or other websites to enhance its content. These are the new blogs.
Wikipedia's got a very nice definition, but I think we're starting to see a lot of blogs that no longer follow the "reverse-chronological" format. More and more trends seem to be moving towards the magazine style look which diminishes the role of your time line significantly by highlighting postings with the use of clean space and imagery. With the magazine style themes, visitors are usually more inclined to browse around the topics that interest them instead of having to page through other posts that aren't what they're after.
A blog (a contraction of the term "weblog") is a type of website, usually maintained by an individual with regular entries of commentary, descriptions of events, or other material such as graphics or video. Entries are commonly displayed in reverse-chronological order. "Blog" can also be used as a verb, meaning to maintain or add content to a blog.