Poser will, as hborre says, create a basic runtime folder. Subsequent installations of files will add new folders as needed.

In my runtime tree I have one for V4/A4 and that one does have a Poser.exe in it, as does my runtime for M4/H4. I have one called 'Locations' which are all the buildings, city scapes etc, which does not need the Poser.exe so doesn't have them.

The reason I have a test runtime is for the old Bitrock auto installers. I send everything there, look at the file structure, move/rename the bits to match my system, then control X the runtime folder, go to the runtime I want that content in, and hit control V, and it all gets put in the right spot. It means I don't have to fishing through the final runtime looking for where the installer put things.

again, as hborre says, files that are zipped often extract into the runtime folder structure. Those I can just change to my own structure then put in the destination runtime.