Commonly, you see the focus of demonstration skills eclipsing the ostensible principle skill - and, in the originally cited example of the guitar soloist, although extraordinarily talented showmen like Eddie Van Halen and Jimi Hendrix might have a lot to answer for, you can't really blame them for the inevitable apists, epigones, and other absurdist tailchasers that followed in their footsteps.
The widespread criticism of Britney Spears' recent performance at this year's MTV Awards also highlights this. Note that nearly all of the sniping comments refer to her demonstration skills - that is, her dancing, her looks, her lipsyncing (the performers to receive good press get complimented on those very same ephemera). Give the girl a fucking break - it's not like her songs are better or worse than anyone else's. Maybe even a bit better.
Of course, at this MTV level, the basic skill of singing a song (let alone writing) was forgotten about a long time ago. It also reminds me of Chris Morris's wonderful The Day Today series that satirised TV news' addiction to endless overblown computer graphics and camera edits that end up superseding the news reporting itself. The Day Today hit its target so unerringly and so accurately that it's hard to watch the real thing nowadays without a sense of profound cynicism.
To me, demonstration skills are absolutely fine, and moreover useful, as long as the original and main purpose isn't lost. The intent.