Opened.
I'm a bit skeptical. It's not like One-Hit Wonder where there's only one metric (one song far ahead of any others) that can be clearly portrayed with one graph; here there are two things the reader must understand. Not sure if the Billboard chart/last.fm layout is clear enough to show that we're talking about rankings versus actual popularity, but I'll withhold judgement till I see an image.
If you want to go the Billboard & last.fm route, Pearl Jam might be a better choice than the White Stripes, because none of their Top 40 Hot 100 entries can be considered among their most popular songs and there's an interesting story as to why that happened in their entry.
My main concern is that it's going to be tough to both separate and connect two different lists, probably with different designs.
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My first thought for an image to illustrate Chart Displacement was a side-by-side of their list of Billboard Hot 100 entries against their last.fm rankings, both showing the top 3 rankings. I think if we can make such an image fit, it would clearly convey the trope.