Henchmen Skills and Levels

Do henchmen get higher in level as you go through the game? Or do you have to party with them and level them that way. (Like your pets as a ranger)

Also, do they ever obtain more skills?

Level 3 henchmen in Old Ascalon are pretty damn useless and don't do much else besides slow down my own leveling pace.

As you get to new locations with henchmen, you will find that they are higher lvl to be more balanced with the lvl of the creatures in the missions/explorable areas. And I am pretty sure they do get new skills depending on their lvls, but not always.