Perhaps if your presentations were to audiences of up to 300+ people in large auditoriums, the work of changing all of your images might be overwhelming.
My presentations are 30 to 40 minutes long with over 100+ images.
To change 20 images for a show, I would have no problem using 16x9.
Fortunately the program has the choice of what format you want to use, I really do not see why anyone would care. (Just my opinion)