I posted once, a while back, about how music tends to "bleed" through different cultures. Music, of course, is fairly universal and tends to get copied from one culture to the next. That's why I've heard zemiros sung to Simon and Garfunkel tunes, among other things.
Steg, in his comment to my point made the following comment:
One of the main points of my presentation was the oral nature of the musical culture; tunes enter into it, and once a few years go by, or the tune becomes popular and passed from person to person, no one has any idea who invented it or where the tune came from — it's all ya‘ni "halakha leMoshe miSinai". That's why you have, as you mentioned, people who would never listen to Simon and Garfunkel or the Beach Boys use their tunes for zemiros.
Of course, there was one aspect that I didn't count on when I thought of that post months ago - the aspect of outright copying. There are times that popular Jewish musicians will outright copy tunes from other, secular sources.
Considering that many chareidi people won't listen to any secular music since the music itself (even sans lyrics) can be metamem es ha-lev, I'm curious how many of them realize that a song that they've all heard many times at weddings is actually ripped off from a German pop-band of the 1980s. The song, specifically is Yidden, which seems to be de riguer at weddings these days. The tune originally came from a German pop band called Dschingis Khan, from their eponymous song. You can view the video for it here.
Will there be a call to ban the sale of Yidden tapes and CDs (and the playing of it at weddings)? Somehow, I don't think so...