I guess they probably include in the term headphones earphones as well. There are huge numbers of eabuds and IEMs under $10 being sold. There are even very usable IEMs under $10 such as the JVC Riptidz. There are a number of IEMs under $20 that sound quite decent. As far as actual headphones though, the only decent one under $20 I have found is the JVC HA-S160. I still say you should review this, as it is imo quite unique.
That makes sense. The sheer quantity of earbuds and IEMs (all price ranges) is overwhelming to say the least. For me personally, just can't use them. I've tried. It must be my 30+ years of using on-ear and over-the-ear phones...
I certainly agree that there is very little worth mentioning in the $20 range as far as actual headphones. I will get around to checking out the JVC HA-S160 as well as the KSC75 (with headband mod).
The only others I ever hear about at that price are the Monoprice (8323,8324,8325). Have you ever heard them?
As you can tell from my reviews I didn't find the Meelec HT-21 or Soundmagic, both $20, to be worth it.