Well, lets put it this way, every game I've ever rented (important, as you don't exactly want to spend £40 on a crap game) has come with a manual, and 99.9% of those looking for manuals don't own the originals. Besides which, if you back the discs up, why not back the manuals up at the same time, thus losing the problem. I appreciate the fact that sometimes used/second hand games sometimes come without manuals, and in this case I can see your point, but if your dogs chewed it, then what exactly was it left out of its box where the dog could get it anyway, lol
I hope you can see my point in here too, just as I see yours...