No, I'm not talking about just auto gear. I'm talking about local decoupling near the active devices. Generally these are ceramic....possibly in combination with a larger electrolytic or possibly a film capacitor. A lot of digital circuitry in audio gear too. 
Whether it's the best capacitor for that job is not really the point. The reason they are ubiquitous in this application is the cost.
I think some missed the real query that Early B is asking about. I think it's clear now that's he's referring to the practice of shunting (bypassing) different value/types of capacitors together in audio signal coupling applications. Probably a high-level speaker crossover network or such.
A considerably different (IMHO) application of the term "bypass capacitor."
Oh well.
Dave.
I referred to both auto and home applications, including antique, if you look carefully.
Ceramincs won't do the job with electrolytics as the ceramic is way too small. As you
indicate it is cheap and cost effective for the bottom line.
It does, however, as I explained in a previous post, help remove RF and other high frequency problems.
It could be near active devices to accomplish this purpose or to help minimize/eliminate
self oscillation by using a "swamping" method. Unfortunately, that is not good
for the audio signal itself.
Yes, it is used in digital areas and probably in the analog audio path, as it works with very high frequencies,
to remove them. This includes RF.
Bypassing coupling capacitors with ceramics is not a good practice, engineering wise, for the
reasons I outlined in my previous posts.
Cheers.
