It's not a belief. Is DOES work with some headsets. But one thing that i noticed is that it only worked when i had OFW. I purchased a cheap headset (Around 100 INR/-) that gave me a LOT higher audio on lineout.
But the same didn't happen in CFWs.
Si it's Real.
There are 2 types:-
Headphones dont have a mic. So u'll have to talk with the phones mic. And Headsets have a mic.
When you connect a head set, the phone will detect it as its jack is longer than headphones. When you connect a headphone, the phones gets confused weather you have connected a headphone or a portable speaker. So it gives you options.
Maybe the creator of many firmwares, add a mod, which sets headphone as default.