I consider my DD self weaned. When she was about 9 months, she started to fuss at a couple of particular BF's that I use to offer. I picked one of those feeds to stop - just not offering it any-more. Basically, DD didn't even notice. She never looked for that feed, happy drinking water from her sippy cup and eating a finger food snack. Another example is my friends 2 kids. One day they just decided (shortly after turning 1) that they didn't want boob at all (for all feeds). I suppose thats an extreme example of self weaning.
My CHN said that you get some babies that are happy to give up the boob and some babies that never want to give up the boob, eventually having to be forced off it. I think it would be really difficult dealing with a baby that doesn't want to give up the boob.
DD is 3yr 8 months - DS is 6 months