On an independent blog, you can't be sure who would be reading it. It can feel as if you were printing out flyers with your thoughts and distributing them in a busy square. It could be a friendly eye, a stranger, or even your enemy that would be reading the flyer. That kind of uncertainty makes you nervous and puts you on the defensive. You feel more self-conscious, and feel compelled to let out only refined thoughts and ideas.
On the other hand, LiveJournal is friend-oriented. You know that your entries will be read mostly by people that care about you, through their friends syndication. It can make you feel at ease, and you can actually
think out loud without having to worry about saving your face or being branded immature. When in doubt, you can even make some of your cruder entries friends-only on LiveJournal.
Now if LJ only supported trackback... :D I'd submit a patch (because LJ is open-source), but I'm too lazy.