Placing the cheesecake pan in a waterbath helps, but not because of the moisture issue. Cheesecake is basically a custard, and custards require baking times that are low and long to avoid overcooking and couagulation, both of which lead to cracking. Since water can't get any hotter than 212F (at which point it evaporates) it acts as insulation to your custard or cheesecake, which helps keep it from overcooking. Place your cheesecake pan in a larger pan (if you're using a springfoarm pan, line the outside with a few layers of foil to prevent leaking) and add enough BOILING water to come about halfway up the pan. Bake your cheesecake for about half to three quarters of the recommended time, then without opening the oven, turn off the heat and let the cheesecake just sit in the oven for the rest of the time. The heat from the water, the air in the oven and the cheesecake itself will continue to bake the cheesecake, and help aviod overbaking.