I was an assistant for a night at my university! I am not an editor, but let me chime on what I've accumulated:
Some pictures are chosen because of who's in it, other pictures for their size or shape (horizontal, vertical, square, etc), some because of what's in it. For PJ, it is more important of what's in the photo than if any artistic component exists. Then too, it depends on what the editor personally likes. (Such as, taking only crooked angled shots at the OSU/UM men's basketball game - I absolutely loathe crooked shots for PJ, and that's all of what the asst. editor wants to do, so she can make up her own slideshows while very few of my events make it. /End Rant.)
Only two of the ever growing number of photographers shoot with Canon; all shoot with digital. For MF and film, you can almost through it out the window unless you shoot something over the weekend and doesn't have to be in soon (assuming the paper only publishes on weekdays). Digital, while maybe not as good IQ size as some film and MF - but you can throw that out the window when shooting sports and how, is much easier to use quickly. Maybe Nat Geo is the only publisher that uses film, everybody elses bread and butter is digital.
So in all, you have the editors' personal preference (like crowd shots instead of dunks), politics, size restraints, who or what is in it, and getting the shot.