Well, I'm probably the wrong generation to even guess, but the biggest functional difference of a blog (weB LOG) is that it's very easy to add comments; almost as easy as responding to these threads. The idea is that you keep a journal and add your thoughts whenever they pop into your head, without having to re-write and re-upload the entire web page.
Beyond that, many of the blogs go beyond one's personal brain ferts and allow others to also add their contributions. Then, there is some sort of network in which bloggers can easily link to other bloggers.
They were used very effectively during the last national elections, because information can be posted on a cnadidate's web site almost instantaneously, counter-attacking where necessary.
Part of the function of blog software is to separate the visual appearance of the site from the content, allowing the writer to forget about formatting his text -- it will all come out looking the way it was designed.
There is also a category of web design software that goes beyond the blog -- content management software or CMS. In this type of web software, different categories of content can be defined and easily rewritten. Instead of just a journal, there may be news, articles, journal, photo gallery, calendar, etc. Like blogs, these can be configured for one person (or one managing group) to do the uploading, or they can be used as community-based software.
I've been looking at the CMS software for a project and have found between 10 and 20 open source (free) systems. The problem is that they are all still pretty geeky, not easy to set up, not easy to design, and don't yet have much in the way of documentation -- at least not enough for this white-haired old fert.
If you start looking at sample blogs, you'll see that most are simple ego-trips. A few have an occasional thought worth reading.
{EDIT} yep, once again a whole bunch of folks responded while I was typing. When I started, no one had responded yet and I thought, "I'll be first!" /forums/images/graemlins/tongue.gif