Comment #3 on issue 2459 by [email protected]: Vertical positioning of Lyrics, Dynamics etc. - breaking into segments
http://code.google.com/p/lilypond/issues/detail?id=2459
I think it's likely to be easier to follow a line of lyrics when they are all at the same level - moving them up and down would, I think, break the ability to read fast. That said, your example is a good one of where doing this makes sense - there is no line to follow. I think this should definitely not happen by default - but it could be possible to make it happen with something like \vertBreak in the lyrics.
