This is an extremely "Leonard" move. I'm thinking of it in much the same way (as I mentioned above) as "very close companion" which sounds almost exactly like "varicose companion". He definitely likes to play with the way words sound, not just their specific meanings. And "tube" is replete with many layers of possible interpretation whereas "tune" would be fairly straight-forward. This is also a great example of how a single word can change an entire song/poem. (I remember one version of "My Funny Valentine" the singer chooses to sing "don't change your hair for me" instead of "don't change a hair for me". This one move completely changes (in my opinion ruins) her rendition of the song. A single word can change everything...)
Anyway, on the surface, "tune" worked very well. That would have made the meaning of the entire song very clear and there would not be a whole lot of room for individual interpretation (many of which may be perfectly valid even if seemingly contradictory; depends on how much you believe in the validity of authorial intent). "Tube" though, listeners will be arguing the meaning for years. I love it!
