Yup ~ the spectrum varies so vastly dependent on personality and life experience .... some children are more 'determined' to try new things and others happy with the 'status quo' so they need to be motivated and gently pushed with trying new things .... also depends on how they are parented some parents encourage and promote independence in infants and others carry them and keep them 'dependent' .... so a child who is down on the ground and left to 'explore' is going to learn to move around furniture and so forth quicker than one who is kept up on a lap and held.

As for what you can do to encourage ~ practice .... if he has spent alot of time sitting or being held he will need to build up muscle control to catch up so playing games that encourage him to 'stand and bare weight' and so forth?