We are not "AAA " here, the majority of the users aren’t even in a studio period.
When you download something from the marketplace, it needs it ‘just work’ as Epic has been explaining. Having price tiers is just fine for other webpages, but not in the marketplace.
Also regarding your analogy:
Yes you pay them for their work, once you have the finished product, and because that deal is complete, I now own the rights to use model as I see fit. When I contracted out the work, I was contracting for the model to be created for me, I did not specify why or where the model would be used, I contracted it out to have it made for me, and once it is complete, the transaction is complete, and I now more or less ‘own’ the rights to that model.
There are different contracts that can sometimes be made up, but rarely is the recipient of the model legally bound to only use it in one project, the majority will never be used again, but not because of a legal obligation, more just that companies rarely re-use assets (the odd one here and there maybe).
They state in the FAQ that you are responsible for maintaining functionality in future engines, the only ones really affects is code based items, as they need to be recompiled for a new version, which is a simple task to perform.
All of depends on what exactly you are bringing to marketplace, but if you really need to have your users pay for more than once for your product, come up with an updated/improved version 2 the next year, version 3 after that etc. But forcing them to pay again for the same product, to me at least, just isn’t right.
It may seem like the business savvy thing to do, but which is more important to you? Getting the highest price for each unit, or selling a larger amount of items at a lower cost? Nevermind the possibility you could get ‘tagged’ as a greedy seller (by the community), now you sell even less units at the higher price. It might seem like price per product is more important looking at it now, but you also need to think about how your customers perceive you, and how likely they will be to support you in the future.