Linode to S3 is not apples to apples. If you want to compare to S3 you would need multiple linode boxes and a system for redundancy in the face of image corruption or hardware failure.
One of the things you are paying for with S3 is a pretty solid guarantee that your files will A) not get lost and B) always be available.
That's a relative term, though. While complete outages are rare, there are frequent, prolonged periods of abysmal performance (latency in the >300ms range, throughput approaching <50 MBit/s) and the average performance without CloudFront isn't stellar either.
However, for many use-cases the sheer convenience and low cost of entry trump these issues.
One of the things you are paying for with S3 is a pretty solid guarantee that your files will A) not get lost and B) always be available.