I don't know anything about how the refridgerator actually works, but the commercial grade refidgerators that most restaurants use have the same effect. In purchasing one for a restaurant I worked at, the salseman told me that the feature you are describing was to help regulate the temperatures inside. In restaurants the temperatures foods must be kept at are very specific. The door is nearly impossible to open when the temperature inside reaches a certain point, this is to give the condensor (or whatever cools your fridge) time to get the temperature back down where it's supposed to be to help prevent food spoilage.

Or, at least, that's what the salesman told me when I asked about it.