[mesoman]

Public funding contributes basic research. Corporations contribute other things, like design for actual use and production, production tooling design, production tooling production, factory space and management, distribution management, warehousing, marketing (yes, you do need to spend money to market it in any economy). And by the way, all this results in paying wages and taxes which go back to the public.

Also, in many cases of publicly funded research, the resulting company is owned or partly owned by the researcher(s), which is one of the incentives for doing the research in the first place.

Utility patents cover that which is new and, in theory, non-obvious (although non-obvious is very poorly enforced based own personal experience). Those would include the "tweaks", which may not be as minor as you think, given the difference between the needs of a product that is to be mass produced, vs. a proof-of-concept laboratory device. Patents might also include the methods of production. Design patents cover the appearance and aesthetics, and are a different type of patent in the US.