I prefer drop bars but I tour with a friend that leaves his drop bar bikes at home for touring, he instead uses flat bars on tour. It is all personal preference. I do not know if the majority of touring bike riders prefer drop bars, we might be in the minority.

The reason that I prefer drop bars is that I like to lower my head and upper body as I push into the wind. But, I will readily admit that I did not like drop bars as much when I weighed 20 percent more than I do now, then it was less comfortable to lean over that much. If I did not use drop bars, I would probably use trekking bars.

Last summer I took a supported tour where the bikes were provided by the tour group. They were flat bars. I found that I did not like the width of the bars, they were much wider than my drop bars.

Check out these bikes, this is a good cross section of touring bikes used by experienced touring riders. (There might be a bias towards more expensive gear at this link, people are less likely to take and show photos of their bikes if they are not proud of them.)
http://www.pbase.com/canyonlands/fullyloaded

If you switch from flat bars to drop bars, you may also need a narrower saddle too.