I honestly haven't done much serious reflecting about what particular musical qualities have sparked these connections. In the case of the Franck, the syncopations perhaps stand out as unusual for a big, serious symphony, which is why that tune always seemed a fish out of water in the concert hall. The Dvořák and today's Beethoven theme just strike me as giddier than usual (not a bad thing!) for their contexts: high energy, some unexpected accents, simple building blocks that make them catchy, etc. I'm sure some would say that adding a "Hooked on Classics" beat to any foursquare tune would make it work as well as the themes I've chosen, but I'm skeptical. It can be hard to shake such qualities as grandiosity, elegance,* and seriousness of purpose. For better or for worse, Dvořák, Franck, and Beethoven have found the secret sauce.
The scherzo of Beethoven's silliest sonata, Op. 31, No.3, has stood out to me as unusual since I first heard it in college (in the 80's!). The first and last movements of the sonata actually have more misdirections and sleights of hand, so they're more comical in terms of syntax and surprise, but the second movement scherzo, with it's bouncing L.H. accompaniment, has the most endearingly goofy tune. I'm pretty sure I always thought it had a "pop" sensibility, with it's combination of smooth melodic contours, bouncy articulations, and a kind of natural off-beat emphasis (not so much from the sf's after beat 2, but in the way the left hand pattern naturally gives a kick on beat 2). It even looks funny to me, I suppose because of all the staccato dots:
I remember hearing Richard Goode perform this sonata live about 25 years ago, and although I suppose people weren't literally laughing out loud, it was the flat-out funniest performance I can ever remember hearing/seeing - funny on purely good-natured musical grounds, not because of lyrics, staging, or whatever. (OK, Goode is a bit of a character, and his floppy hair was a character of its own back in 1989.)
I've been disappointed in looking for a performance on YouTube that captures that unpolished spirit, though I like this one by the always interesting Lazar Berman:
Berman's approach is still more "studied" than I'd like (I'll get to that in a second), but it strikes me that the humor of this movement has to do with how all those semi-serious diversions, pauses, and hints of turmoil always end up back at the same silly, banal place: the irresistably "easy listening" tune.
To be honest, my conception of this music was changed forever when I first heart Don Dorsey's synthesized "Beethoven or Bust" album, also back in the '80's. The whole album screams "'80's," and I recommend it as a highly entertaining artifact of its time. (The "Rage Over a Lost Penny" is a great starting point.) I wouldn't say this album has "ruined" the Scherzo for me, though; rather, it's revealed its true destiny in a way that makes every well-intentioned piano performance a little disappointing.
Whereas I did the synthesizing of Dvořák and Franck on my own, I didn't really feel like I could improve on what Dorsey had already done with this Beethoven scherzo (subtitled "Western" on the album), so I've simply made my own 30-second cut to close out an episode of "Charles in Charge." Just for the record, I've never watched a single episode of "Charles in Charge," but it seems like the embodiment of '80's TV at its most '80's, and the Beethoven/Dorsey Scherzo is a perfect way to cap an episode. (Also for the record, "Charles in Charge" may have one of the worst theme songs in TV history. I'll let you do the legwork finding it.)
So, that's the end of this series for now. I've even made a little YouTube "composerTV" playlist, with a couple of bonus additions from the MMmusing archives. Hopefully all of these tunes will find their way into pop culture one way or another.
* "Elegance," for me, is where Haydn's famously light-hearted themes fail the "80's" test - that is to say, the Haydn comic tunes are too elegant.