re: long term campaigns
The idea of the "campaign" to my knowledge comes from the wargaming roots of the hobby.
Gygax seemed to think of a campaign as such:
Moreover, each session was probably longer, taking up the larger portion of an entire weekend day. This idea has survived in trad games, where you might be playing with more or less the same characters using the same system for at least a year of weekly play (Horror on the Orient Express, etc).
My sense is that more recently-designed games have moved away from this model. Not that they are limited to one-shots, but also that they are not designed with slow, long term progression in mind, and instead think of "campaigns" as "seasons" (as for a tv show) or shorter arcs.