Who says artists don't benefit from used sales? Just because they don't make their two cents royalty doesn't mean they don't benefit. Performers don't get paid for having their music broadcast on FM radio, but no one would argue that a performer is receiving no benefit just because s/he didn't make any money.
If a record is constantly being scoured for, and people continuously buy it, there's a reasonably good chance that some record company will buy the rights (cha ching) and re-release it (double cha ching). If it looks like a product has some sort of commercial value, someone somewhere will release it.
Let's not forget the obvious benefit to a community of having a profitable business. Record store owners have bills, too, and if you buy a record, it might leave them with enough money to stock new records. It might not benefit that specific artist, but it benefits the culture.
Besides record/CD stores have massive overhead to cover, they make more money from a used CD sale than a new one. So those used CDs are what's allowing these record store to stay open and stock new music by other artists.
But on another note, the idea that someone bought a record and put it online being the same thing is a faulty analogy. Only ONE person has to buy a record ONCE and put it online ONE time. That's it. A thousand people, or a million people will download from that ONE measly purchase. That's not nearly the same as a market for reselling records. If a store sells 100 used copies of Nirvana's Nevermind, then 100 copies were definitely bought at one time or another.
EDIT: I use the term "record store" and "records" and "CD" loosely. What I'm really referring to are music vendors and the different types of media they sell
I was a record store employee for about 5 years, I can attest to the fact that we always stocked new versions of albums we sold a lot of used copies of. The used market is a great measure of demand for a product. We could risk buying a used obscure funk CD for $2, sell it at $5 or $6, and if it moved fast, we knew that it was probably a good idea to try and stock a new copy of the album.
Think about it like this: in a record store, every new CD (record, video, whatever) must sell at least 2 copies in a year to "pay the rent for the shelfspace" meaning that if something didn't sell two copies last year, it's wasting space and costing money. Trust me, outside of the very top mainstream, very few CDs move 2 units a year in one store. Something like only 5% - 10% of the total stock. Luckily, that 10% sells maybe 2 copies *a week*, and is thus "paying the rent" for all the CDs that don't sell. But no decent record store only stocks mainstream hits, you need that more outsider stuff because people who buy outsider music tend to buy *lots* of music. So a lot of record stores cover the cost of their genre specific music by selling loads of used CDs. (The average profit on a new CD is about $2, but a used CD can net $4 or $5 profit. You do the math about what's keeping the vendors, and thus the suppliers in business. Also remember that most labels/distributors don't accept returns for stuff that doesn't sell, so once a CD hits the shelf, the artist already got their money)
