APERTURE > PS file size
because when you send a RAW file from Aperture to PS, it has to export a TIFF file for PS to be able understand it
same thing will happen if you take a RAW through ACR into PS... the resulting PSD file will be bigger than the original RAW.
A raw file has one 'brightness' value per pixel (either a green, blue, or red one), a tiff has three 'brightness' values per pixel (red, green, blue). In a sense you could see a raw file as a lossy compression of a bitmap image (in reality it is of course rather a lossy 'sampling' of the image the lens projects). Additionally tiff files at this stage of processing are usually 16 bit files, whereas raw files are 12 or 14 bit.