I think you misunderstood. They're not saying S3 uses a million hard drives, they're saying that there exist some large single buckets that use a million hard drives just for that one bucket/customer!

actually data from more than one customer would be stored on those million drives. But data from one customer is spread over 1 million drives to get the needed IOPs from spinning hard drives.

There's likely over a trillion active SQLite databases in use right now.