I don't think this robs Bowie's music of some it's impact. It just hits another part of the brain. While lyrics which are clearly interpretable (is that a word?) will make you think about a topic, Bowie's lyrics are rather about "feeling" the topic. So rather than knowing what the the lyrics are about it is possible to feel what they are about, but that not less exactly. Perhaps this is comparable to Picasso's Guernica (I love to take this painitng as an example for pretty much everything...) - it is clear what it is about but rather than describing an accurate picture of what it looked like or what it was about it just shows an expression of the feeling created by the incident.
The important thing is that there ARE connections between the song and a topic. So the song is about something. Or at least one can be sure enough that there is something in order to see it as a riddle. The moment a song would be about nothing but just collection of images it would get completly uninteresting on every level except perhaps the dancability or other madonna-esque qualities.
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