What these questions overlook is that it is not the actual work of the designer that is being sold. The analogy is more akin to the resale of comics, where something that once cost a dime can fetch thousands or even millions of dollars. I don't think anyone has ever suggested the people who created the comics should get a piece of that. (Tho many fans seem to assume we do.)

But when it comes to the original art, then there is a unique object that is being sold and resold, and that is where "royalties" should be considered. (And, yes, I do think this should also apply to "fine art." When a painting or sculpture or whatever is resold, the artist, or his/her estate should receive a royalty.)