Executive Meddling: Several songs were purportedly chosen because Nintendo of America president Reggie Fils-Aime liked them. In addition, many rumors of a sequel exist purely based on the fact that Reggie was apparently quite fond of the game. Not that him getting us a sequel would be a bad thing.
In fact, it seems that "September" and a Jamiroquai track have to be in every music game Nintendo has some hand in, being as they are in EBA, Donkey Konga and... well, that's it.
"September" and "Material Girl" are also in Wii Music.
In a strange story example, you can see a small cameo by what looks like Tsuyoshi Hanada from the first Ouendan game in the New-York themed "Sk8er Boi" level. The dev team then decided to make an entire scenario in the sequel that explained how he could have gotten there. It would be The Producer Thinks Of Everything if 1. it wasn't a game, and 2. the developers were even expecting a sequel to Ouendan at all.
Hey, It's That Guy!: A few characters from Ouendan appear in this game, especially noticeable with the lead actor in Romancing Meowzilla, who previously appeared as a character in both Ouendan games.
Hey, It's That Voice!: The covers of "Walkie Talkie Man" and "Canned Heat" are sung by Jason Paige, best known for his first-season Pokémon theme.
The cover of "Sk8er Boi" was apparently sung by the same person as the theme song for Kim Possible.