George,
I'm not ready to go along with the assumption that all commercial digital repositories charge a "per-chunk, per-time-period fee". There are many cost models for these types of service, based on the Service Level Agreement agreed to by the repository and the customer.
To assume "if you don't keep paying your data goes to the bit bucket in the sky", well, isn't the same true for gas, electricity, water, etc? Not quite sure I agree with the statement - and it would seem than anyone using an outsourced digital repository would have physical backups of the data somewhere else, if a proper disaster plan is in place.
Are university systems inherently less prone to disaster?
I'd like more help to understand why university repositories in general are superior to those in the commercial space (and have the implied "added value" of existing in perpetuity).
Best, John