You certainly seem to be providing me a soapbox this week!
There seem to be two general factors affecting the relationship.
1) How close the groups are organizationally speaking, and the overall attitudes of their management – meaning whether or not they have been set up to be adversaries.
2) Whether or not the groups work together on a regular basis solving problems – Which allows mutual respect to develop.
My personal take on the relationship business is that if people take the time and effort to treat their colleagues with respect, that goes a long way toward making things work better.