I had noticed that and forgot to put it in the post! I should do so. I'm sure cathexys has developed some typology of crossovers. The Brimstone one was a name-check, and like the Real Genius story it added an in-joke, as opposed to being important to the plot. The Nip/Tuck story worked for me because the due South mythology, imported to Nip/Tuck, yielded great results for the Nip/Tuck characters, which seems like a decent reason to have a crossover. The Calvin & Hobbes less so, and your explanation makes sense, though that particular story might be someone just trying to reach out to SGA fans.