[MENTION=7175]jadrax[/MENTION] post about Mearls using rock rules from giants is probably a bunch simpler to use and makes sense.
While I would not see a cat using throwing as an attack, I have seen cats catch a rodent with their claws and fling it up into the air in one motion. Not sure that really adds anything to the conversation, but it sure was fascinating to watch the first time.
I've also seen cats get their paws into something that they shouldn't, get scared or injured, and whatever it is goes flying. But, I don't count that as throwing something at a target and I also really don't count it as taking a foe, throwing it into the air, and having it take falling damage. For one thing, there are few cats large enough to be able to throw small and medium PCs up into the air.
But I do think that for a large enough giant, grabbing a PC in one hand with one action, and throwing him straight up into the air with another action, is perfectly reasonable. Now the DM just has to figure out how high up into the air a giant can throw a medium PC (who typically weighs in at about 250 or so pounds with armor and gear). A huge 25 Str giant can lift weight of 30x25x2 = 1500 pounds with two hands, so presumably 750 pounds with one hand. So, how far can such a giant throw a 250 pound (with weight and gear) medium sized PC? Probably 5 or 10 feet above the giant's height and reach. So for 20 foot tall giant with a reach of 15 (assuming a huge giant can be that tall, I do not have the MM in front of me), he could only throw a medium PC about 40 or 45 feet or so into the air, maybe 60 feet away from the giant (similar to how a man who can lift 200 pounds with 2 hands could probably only throw a 33 pound object 10 feet into the air and 15 or 20 feet away with one hand). Rough rule of thumb. Alternatively, take the average rock weight (I assume rock weights are in the MM) times the max distance a giant can throw it and divide by the total weight of the PC. That will probably come up with a smaller number, but it could be used.