It might have been me who originally uttered the statement which gave rise to this thread. The distinction was a bit different however. Originally I was of the opinion that drop bar touring is an anglican thing whereas flat or straight bars was mainland european. Of course it is not as simple or black and white. Then again one would be hard pressed to find a drop bar touring bike from the larger mainland european bike brands.
One can only guess why the distinction exists, but I would speculate it relates to the more relaxed approach regarding cycling in general in mainland european countries as opposed to the british isles and north america. But the reasons can lie elsewhere as well.
Personally I'm ardent for the drop bar. I've tried the flat, the north road, the denham, albatross, wide gravel drop bar and I keep coming back to the shoulder width drop bar. I have however found that a 12 degree gravel flare is a significant improvement so I've swapped that to all my drop bikes. The benefits of a drop bar bike are well know as there's more hand positions, etc. But they are also more stable at speed as they allow for a better rider weight distribution over the wheels meaning more grip for the front tire. They are also the best bar shape for aligning arms and hands in the most relaxed position meaning they have the potential for least neck and shoulder issues. All of the aforementioned benefits require however that the bike used is sized correctly ie. short enough reach.
Of course they're not great for tough or loose offroad but for that there is the common flat bar.
I've found that the denham bar and its ilk combine the worst of the flat bar without any of the benefits of the drop. You usually want your most efficient position to be the one where you can reach the levers and grind away the kilometers. Or to put it in other terms, you want your longest position to be your best overall position. With the denham bar that's the wide position. If you size frame and stem reach for that position it means the long bullhorn position meant for headwinds etc. is way too long and uncomfortable and thus unusable. If you size reach for the bullhorns your brake position is too short and unstable.