Runny bees is a genetic trait that is highly expressed in AHBs. Not to say that all runny bees are AHB, just that there is a gene that controls that behavior. So genetically speaking, all bees have that gene, and it is to what extent it is expressed, equated into the behavior being seen or not.
It is not a behavior you want in bees. Not just from a beekeepers desire to not deal with it, which I agree can be irritating and not fun. I know finding queens from such hives is sometimes nearly impossible as the queen flees with the bees bubbling up and over the sides of the boxes.
Here is a practical example....Bees in the fall or winter are bothered by a pest such as a skunk. Instead of the normal few guard bees sent to check the entrances, all the bees decide to "run" off the brood as seen when you open the hive. The chances of brood damage in colder areas increases dramatically from such bees. And hive survivability can be impacted. Bees so willing to leave the brood is not good.
The trait causing runny bees, which is highly expressed in AHB, may closely impact absconding traits on an increased level, as well as swarming or supersedure. These traits in purely warm areas would naturally have no or low impact on such things as brood, and survival chances for the colony. But bees that "run", abscond at the drop of a pin, or supercede in attempts to "correct" perceived problems, are something not good for most areas that experience cold weather, and for beekeepers in general.
Runny bees, is one of the items on my queen evaluation form.