They are digitally scanning them? What knowledge is being lost here?
There's little difference and I would suggest there's a pity in knowledge being hoarded by collectors.
If we were getting into the differences, though, it would be that is now happening en masse in order for a handful of corporations to monopolise knowledge, history and ideas from books that were until recently available somewhere to the public.
I also doubt that many collectors are buying rare books with the intention of destroying them.
And it's irreversible when the books are really destroyed.
That combination makes it an urgent and important issue.
Or do they keep it on their private, warded off storage?