Sarcasm notwithstanding, you know what the term describes and you started a thread on the term a couple months ago and it was explained very well.
http://www.bikeforums.net/touring/10...avel-bike.html
This also is around when you began deriding the activity by mockingly calling it 'grrrrravel grrrrrrinding' for some reason.
Neither your hybrid nor your mtb are inadequate. Nobody has claimed they are(except you, sarcastically) and in fact I specifically mentioned youve been doing the very thing that is currently a niche, so clearly that upright hybrid of yours works quite well.
You claim that such a style of riding demands a new bike, but that isnt accurate and you are smart enough to know it isnt accurate, so why even make the claim? While it doesnt demand a new bike, a new bike may be beneficial. If someone has a couple road bikes which max out at 25c tires and have road double gearing, that is probably not conducive to ride many of the types of gravel around the country as the tires would jump and deflect all over the place. Plus, the more aggressive frame geometry may not be comfortable for 3 hours of bumpier riding. So in this instance, a different bike would be a good decision, assuming they want to dedicate the time to make the purchase worthwhile.
I could ride my road bike on some rolling single track and do most of it, but that isnt close to ideal. Instead, a mtb with lower gearing, a higher bb, and some fatter tires will make the experience more enjoyable.
Apply that to riding on gravel.
You do it with a hybrid. I do it with near 25yo hybrid converted with some drops. Others do it with CX bikes. Others do it with the currently popular all around drop bar bike frames. Riding on gravel can obviously be done with many different types of bikes. But that doesnt mean there shouldnt be a genre of bike which is marketed for gravel.
I dont expect any of what I just typed to change your mind because it appears you are proud that you do things differently from the lemmings who follow the latest trends in cycling mags. I just dont understand the vitriolic mockery directed towards those who dont conform to your view of how cycling should be.