it seems some satellites, or orbital slots, are more focused on either Direct-to-home (117W, 97W, 34.5W, Anik, 1W, 13E, 19E, etc), mostly in Ku, or on Cable feed (like 105W in Ku). Those won't usually "waste" those prime locations on feeds, when they can rent for big $/€
Then there are the more "utilitarian" slots, that are either used with permanent channel feeds that are not focused on individual reception, or for occasional feeds. Looks like in many cases, big users have reserved transponders, like CBS and FOX on 99W Ku, etc.
Do they always use the southern-most satellites? I don't know, but I would guess they try to stay not too far from it, but also need to take into account the local topology. For example, uplinking from a truck in a large city might mean you have a very limited view of the sky, due to surrounding buildings. In that case I guess they use what they can, and that might sometimes be a bird much lower on the horizon. Also, a large part of the US does not have much in terms of southern-most satellite that would be carrying wild feeds. From here, in CT, the closest might be 87W, that's 14 degrees away from our longitude