On your recommendation I've thought about it again, and I still disagree.
I think that you are now confusing separate issues: access to deleting names, and access to registrar threads. Snapnames/NW/similar might have access to threads locked up, but they make that access available to the public, via several different models. Compare that to registrars who either grab deletes for themselves (prohibited, but done all the time), or enter exclusive, secret deals to grab deletes.
Through services like Snap, NW, Expirefish, I and other general public types have the technical ability and the necessary access to at least some registrar threads to acquire deleting names. Even if I had the opportunity to purchase access to those threads, how would I get names? Its not like 99% of us have the funds and/or technical know-how to make our own registrar deals, like some.
By your logic, any operational business model involving an exclusive partnership is bad because it precludes all other business models the parties involved could have enacted. This makes little sense. As for the registrars that work for Snap, I somehow doubt they would agree that their resources are being used by Snap to their own detriment. I would bet that the dinky registrars Snap tends to work with for the most part lack the ability/resources/time to do anything themselves with their pool 3 threads.