People vary in the amount of sleep they need. I need about 7/7.5 hours at night. My sister needs at least 9. There is that optimal length of sleep for everyone, and it varies from person to person, and baby to baby. So if your baby is happy and alert while sleeping "only" 10 hours at night, then that is likely his optimal length. As you drop naps, you can most likely shift more sleep to the night.
Of course if you baby is cranky and sleepy after 10 hours at night, he likely needs more. So work on figuring out the reason he isn't sleeping the optimal length for him.
Just remember, if your baby doesn't need to sleep 12 hours at night, that doesn't mean there is anything wrong with him or anything you are doing wrong. It just isn't what he needs.