For text-mode this is indeed true, when using a select all you get formatted text, but in the previously stated modes (move or selection mode) I was able to preserve the layout.
EDIT in response to the slightly faster posted previous reply
No, it is not the same. Cmd + 3 activates the selection tool. When you have selected you can use Cmd + C.
Please read again. Cmd + 3 activates the selection tool!!!!! It is a tool to select a part of a page in Preview. Then you use Cmd + C if you want to copy the part that you have selected with selection tool.
I think we have a misunderstanding, cause you seem to be agitated by what I wrote (which was not my intention).
It's probably because of when I said:
I guess it's exactly the same thing as a CMD+A, CMD+C, CMD+V.
When I meant to say: The result is exactly the same when I use a CMD+A, CMD+C, CMD+V (in selection or move mode/tool) in comparison to using the selection tool/mode and select the entire page and copy/paste.
Or do you mean something different?