Here's the answer: Your dog doesn't need more than two toys. Rotate them, so he doesn't get bored. But remember: We're talking about an animal that eats the same food, day in/day out. And while your dog needs mental stimulation in the form of play and obedience training, they will be perfectly happy with chewing on the same toys, for years.
(Much the same way young children can watch the same Barney movie 100 times without getting bored!)