To my way of thinking, cat food is not a non perishable item. The unopened can is a protection that is gone once you open the can. I would not leave my own food from a can at room temp so I do not leave the cats' food at room temp.
If you think of the ingredients, meats and fish are perishable, so if you would not leave a chicken for yourself out on the counter all day or for hours, then you would not want to leave some opened can of chicken cat food out.
I know that it would not be for a long time, but still, the possibility of spoilage and how it may affect a cat's insides should be considered. Ya never know for sure, so I error on the side of safety.
Now that Oliver has joined us, I don't think I will ever have to worry about storing excess food; he cleans his dish then heads over to Shadoe's, so entire cans are put out here now, but if I do open a big 12oz can, it gets put into the frig after putting some out for Oliver.