Dvi files, which TeX outputs, do not contain information on paper size (such as A4, B5) or orientation (such as landscape). On the other hand, in dvi files by LaTeX, these information are specified.
Sometimes even if a dvi file does have a size entry, it may not be the actual paper size. (It may even be zero!) This is why dviout does not set the paper size automatically from the dvi file.
It is up to the user to specify the paper size and orientation in the Property Sheet->[Paper] page or use dviout specials.