I think Oak explains it much better than I do, although she is definitely more coordinated than me!
I used down tube shifters in the 80s and had no issues, but the feel of the bar ends was different. Plus, I'm probably the most risk averse of everyone commenting. In the end, I knew I wasn't going to be doing unsupported touring, and wanted the bike for low gears and the ability to carry a pannier and trunk bag.
I must say, my experience at Harris Cyclery, where I tried the bar ends, left a lot to be desired. I thought it was going to be a visit to a hallowed shop of cycling lore, and I found them to be condescending to my expression of concern about the bar end shifters, as well as lacking knowledge about fitting a short woman.