I personally don't think it's necessarily been 'trained' into him to want you, or that he's being manipulative because he's 'gotten away' with getting what he wants. I think that there are a lot of personality differences between children and that one method won't work for all of them.
My 5 year old started to sleep well at around 3 years - she'd previously been a very restless sleeper and needed parenting to sleep, comforting in the night, etc. In retro spect I think that a dairy intolerance contributed to this.
My just about 3 year old has been sleeping much better the past few weeks. She is very much my cuddly baby - she loved to be snuggled in the sling, held, etc. She would sleep fine as long as I or dh were with her - we had a double bed in her room and one of us generally ended up there at some point during the night. I was starting to think I'd never get a night in my own bed again, but she's generally sleep through now. She just had a high need for touch. She actually also slept well when her big sister would sleep with her, but the oldest didn't like that - she likes her space.
My 5 month old has put herself to sleep from birth and will fuss if she's being held when she wants to sleep.
My point is that all three were different, with different needs. When their needs were met, they were able to learn to sleep on their own.
YMMV, but I hope that helps.
Erica