This has been my experience as well. I've now shared my life with 5 over the years and they're all different. I just them them be who they are. My first one was fresh off the track and had a rather reserved nature at first. He warmed up over time and became more playful and light-hearted but wasn't a needy or clingy type. My second was a major "mama's boy" - definitely needy and clingy in the beginning. He also had separation anxiety and couldn't be left alone. My third was a senior who had lost her first home due to divorce. She moped and grieved for weeks. Then just when I was afraid she wasn't going to get over it she decide to trust again & gave me her heart.
The two I have now couldn't be more different. I adopted Carly in May 2006. I knew she was very shy and anxious when I took her home. She didn't want to leave the safety of her crate for at least 6 months. Four years in, she's made a lot of progress but it's been slow & definitely on her time table. Carly cannot be rushed or pushed. She's still shy & quirky & doesn't like change, but she's happy and comfortable with our routine & I love her just the way she is. Now Princess walked into my house fresh from retirement, checked everything out and then just made herself right at home. She's a happy social butterfly kind of girl. Nothing stresses her out. She likes lots of attention and doesn't mind demanding it. She would have gladly taken over control of the entire household if I'd let her. We've made an agreement though - she can be The Princess, but I'm the boss.
They're all individuals. Try not to worry & just enjoy watching his unique personality unfold.