How does a soft drink not foam up as much when you get it from a soda machine the way it does when you pour it out of a can or bottle?

According to this site in the troubleshooting section the cause of too much foam in a machine is the system pressure which is connected to the carbon dioxide supply. So its regulated in a well maintained machine.
http://www.ebay.com/gds/How-to-Fix-a-Soda-Dispenser-/10000000177634389/g.html
If you pour slowly it won't foam up; its when you pour too fast the foam is in half the glass before the contains is empty.

Yes, pouring slowly reduces foam but I still wonder why a machine that can fill a cup in a matter of seconds does not foam up as much. Perhaps cans and bottles are over-carbonated for better "shelf-life" as opposed to soda from a dispenser which is intended to be consumed immediately.

The carbonation and the syrup are added in separately. Actually, it's syrup, water, and the carbon dioxide being mixed together. How fast the carbonation goes in and how much is regulated by the store/restaurant that is serving the soda. Since it increases food cost to serve foamy sodas, the soda systems in half way functional restaurant are checked often, sometimes more than once a day minimum.

Not the best reference, but it explains how a soda fountain works:
ehow.com/how-does_soda-fountains-work.html [no longer exists]