I breast fed DS till 29 months and he is is one of the most secure, independent, outgoing kids I know (really, I'm not biased

). I know people who didn't breast feed or weaned early and their kids are extreemly clingy. Kids have different personalities and a needy child is not made to be needy because they are allowed comfort objects, whether it be a paci, a stuffed animal or mommies milk.
I know you are making your statement based on your friends experiances but from your description it sounds like there are other issues going on in those cases than just extended breast feeding. I think you will find, if you are interested in reasearching, that extended breastfeeding is believed to make children more secure and has a positive psychological impact.