DS1 was only bf to 18 months, but he was, and is, anything but clingy. He's never been clingy.
From what I know, hercules's views are the current belief - if children are secure that you will always be around, they don't stress about you going away for a few hours here and there, or longer. DS1 went to nursery from 9-5 from 1 year to just over 2, 2 days per week.
I wonder if clingyness is about genetics, or about environment and parental expectations (probably both, to be realistic). I expect my kids to be brave and outgoing and sociable, and ta-da, they are. I like being out in noisy busy places, and I like my kids mixing in with crowds of people. They both like these things. But then again, both DH and I are pretty sociable and brave, so maybe that's it.