I could create a blog and test it for myself, but don't want to waste a username for someone else with something I'll likely never use regularly. I know some of you have had them. I initially was turned off of blogs and onto LJ because at the time, I never saw a single blog with a comment feature, and I liked the comparative social interaction of LJ. I also really like the convenience of the software client (I use Semagic) for updates.
It also seems that blog authors tend to be publishers rather than diarists. Meaning that they write for publication, articles or essays . . . of course, there's stylistic crossover. A statistic I read also suggested that the average age of the blogger is higher than that of the average LJ user, and, as the content of many blogs I've seen seems to be more mature, I'd say personal observation bears this out. It makes me wonder why: what made the older crowd choose blogs instead of LiveJournals? Obviously, as both have become more popular, the age range has broadened, and the generalizations I'm speaking of aren't quite as skewed, but it is nevertheless interesting.
On a more minor note, just speaking from my anecdotal observation, the LJ folks seem to be a little more tech oriented. Maybe that also has to do with the youth factor, and an age group that has never existed without CD players or cell phones.
When I started my LJ, back in 2001, I was writing a lot for WomenGamers, so that was where I published; this journal is, and remains, more of a diary/message board synthesis, and I'm quite happy with it. I feel no real inclination to change: it's more that I'm curious about how the other half authors, so to speak.
If you know about this or have an opinion on it, I'd really like to hear your perspective.