Again, spec out a multi-data center server + storage + staffing deployment and calculate the full cost per gigabyte. As I said earlier, if you buy enough storage you will definitely hit a level where you can beat S3 by a fair margin but many places never reach that point and many of the ones who do are going to have other projects which make more sense because they offer a high rate of return or provide something which isn’t a commodity.
That's a good argument that at a lower amount of storage you won't save money at all.
This is very different from the idea that the savings are a few percent. In almost all cases the savings are nothing or a large fraction.