I strongly suspect the key connection here is insulin response. Eating slowly is probably akin to eating foods that do not cause spikes in insulin levels. What leads me to believe this is that there has been a study (sorry, don't have the link) that changing the order in which you eat certain foods as part of one meal has a similar insulin dampening effect.

Sure. I think it probably works due to my own experience, but slowly sipping milkshakes all day is not going to make you slender. Obesity has multiple causes.