Mm, I disagree. In the case of "I'm on a Boat," any situation would work as well as being on a boat -- that's the whole point, the juxtaposition of the hip-hop video theatrics with something we haven't been conditioned to think of as theatrical on its own. (Although actually, a more mundane situation probably would have worked better -- like, "I'm on a Subway," or "I'm in a Reasonably Priced Mid-Size Sedan.") In the case of "Combination Pizza Hut and Taco Bell," the fact that they're at that particular combination of fast food restaurants (and that that combination exists is important -- "Combination Starbucks and Chipotle" would have been an entirely different song. The thing that's happening is integral to the subtext's existence in both cases. If that particular thing weren't happening, that subtext wouldn't exist.