A vacuum packaged bag definitely excludes more air than a regular packed plastic bag - many of the bacteria which can grow on food and cause food spoilage are "aerobic" bacteria - they consume oxygen as they process the sugars, fats and proteins in food. This is especially important when storing foods for a long time, which is why vacuum sealing is important for long term storage. Another ways to discourage bacteria growth are dehydrating (removing all water from the food as the process of osmosis would pull water from the insides of the bacteria cells; dried apricots are an example).