anyway.

This makes CS go "my own view"
The best long games have a power and meaning that I simply can't imagine finding in a short game. Long games that don't work well are hard to end (because of the investment of time and energy and the hope that they can be fixed, and because of the issues involved in telling someone you don't like their creative work). Short games I have less familiarity with, but they seem capable of delivering punch that is hard to get in a long game. Their limitation seems to be the risk of shallowness or over-simplicity.

This makes XP go "Comparable to fiction"
I think it's like short story v. ten-book-series. You can get something great about getting to know characters if the series is really good (like GRRM's); but short stories or single book stories give you closure on a more specific topic. I don't think 1984 would have worked well as a six-book, 600,000 word series; but similarly, I don't think the Song of Ice and Fire would have worked as a short story. They're fundamentally differently oriented.

This makes BL go "What Christian said"
AKA XP. I think it's really important to note that the never-ending campaign is not the equivalent of a novel. Novels are actually quite short, especially novels from the last 150 years. The long game is equivalent to the super-long series writing.

This makes JBR go "One's long, one's short"
I really don't see any distinction besides one is long and one is short. A short game can nail a character, develop her, and tell an "epic" story. A long game can have great thematic punch. The only difference I can see is length (and how many different games you get to play in a given year).

This makes CS go "Realtime is a big difference"
I generally agree that it is similar to length issues in other forms of fiction, but I see one very big difference: A writer can easily spend months writing a single short story, or churn out a novel in a week. I have read an author comment that he quit writing short stories because he realized it took him as long to write a short story as it did to write a novel. In roleplaying, the amount of time devoted to creating the game generally matches very closely with the amount of time spent in play. A longer game has more time devoted to creating it than a short game. While a short story has a huge amount of time and effort devoted to making each word count, a game is constrained by the amount of time spent playing. I imagine that this is part of the recent explosion of decent quality short games, as a huge amount of effort gets devoted to crafting games that can manage to make a good short story. The time is devoted to the game structure independent of the game session, so the individual session benefits from far more time than players would be willing to devote to creating a one shot for themselves.