Personally, I would argue that the most important principle to protect the customer is that they should get what they pay for when they choose to buy a product. That product should not then be retrospectively nerfed through software shenanigans, either for them, or for any future owner they sell the product on to. This is one idea that car manufacturers have been flirting with recently, and IMHO we should stamp on it hard.
Another idea, but to me a clearly distinct one, is that a manufacturer of a combined hardware/software product might develop software-only improvements after the product has been purchased. In this case, I would distinguish explicitly between fixes for problems where the product wasn't performing as expected at the time of purchase (things like safety issues or security vulnerabilities that clearly shouldn't have been there in the first place) and enhancements (things like performance improvements or additional functionality). Again IMHO, the former should be supplied free and unencumbered to all customers, as they are essentially fixing a defective product. For the latter, I don't have a problem in principle with the manufacturer charging for the upgrade, as potentially it incurs additional costs and risks, and it brings a genuine benefit to the customer that they didn't have at purchase time.
A third idea is a manufacturer deliberately shipping a product that isn't using the full hardware capabilities because of artificial software limitations. They might also then offer upgrades for sale later, which is really just a special case of the enhancements-after-sale idea above. Once again IMHO, charging for these enhancements is still OK even if they manufacturer knew in advance that they might ship that software later on, as long as they were honest about what the customer was actually buying at the time of purchase and they didn't claim or imply that those enhancements would become available for free or on any other specific terms that they don't then honour.
There are at least two good reasons for taking this view. One is the general principle that if someone has bought a product of a certain specification for a certain price then that transaction is then concluded. Just as I don't think the manufacturer should be allowed to move the goalposts after the sale in a way that harms the owner, I also don't think the owner is entitled to free extras from the manufacturer that weren't part of the sale. The other is the practical reality that hardware+software products are enormously complicated, software is never perfect, and the idea that a manufacturer should be liable for not shipping optimal software from day one or prohibited from continuing to do work that might develop useful improvements that benefit customers in return for further revenue is kind of silly if you think it through.
One very important issue I'm glossing over here is whether the terms of the original sale were fair to the customer. This is a standard problem in any sort of retail environment, and we usually rely on some combination of competitive markets and government regulation to protect the little guy. But these are also separate issues to the ones above that would have to be considered on a case by case basis.
