There are some companies who make movies that are always 2hrs 19 minutes long. Evil Angel is one, Anabolic and Diabolic are two others (but some of their lines are shorter). I've always assumed that these companies first edited a movie for content, which would typically be longer than 2:19. Then they would do a second edit to get it down to the maximum running time.
It appears that, with the Director's Cut DVD's, that second edit doesn't take place.
There are rarely Director's Cut and non-Director's Cut versions of a movie. What sometimes exists is a Collectors Edition (or something like that). Private has done this with a few of their movies. Typically, these editions will have an extra "bonus" disc containing "Behind the scenes" footage or will have something else in the package (like a booklet). When this is the case, stores either have to decide which version to carry, or whether they should carry both versions. They will make that case on what they think they will sell best.
Stores will usually identify which version they are carrying because the prices will be different.
The last situation is one that usually affects older movies. There have been some legal fights over who owns the DVD rights to some movies. So Company A (who may own the VHS rights) releases a movie. Company B, who really owns the DVD rights, stops Company A from selling the movie. Company B then goes out and does a better job restoring the movie and adds things like a Directors commentary. They end up calling the movie a "Director's Cut" even though the movie might be identical to what Company A distributed.
In this case the stores will probably sell their inventory from Company A, before stocking the version from Company B.
[Link]
