When they were created, the tablet version was made as a smaller file as it was intended for a smaller device with a smaller screen and less power. Simple as that. Sometimes versions for laptops are produced at slightly higher level of detail but in most cases the human eye really can't tell. I even go so far as to use 3rd party software to compress my pdfs even more as they open and scroll very quickly, which is what you need for rulebooks. I spend almost no time at all zooming in on the pictures. A pdf's size is mostly about the images, not the text, so don't worry, nothing is missing!