While I agree with most of the points made by Corymbia and Amstel, I do strongly feel that cribbing leads to gas colic. Horses can't burp up the air that they swallow when they crib, just like they can't vomit.
On page 18 of this report (translated):
"For a very long time it was assumed that the air that enters the esophagus was indeed swallowed, (Holmes, 1839) and it was the generally accepted view for a long time. However, research by McGreevy et al. (1995b) showed that only a very small portion of the air actually reaches the stomach. The bulk of the air exited the esophagus through the throat cavity and the distention of the esophagus disappeared. Additionally, the swallowing motion of the tongue normally visible when the horse swallows was not observed."