[johnkmcnabb] I think I have some answers for my own question:
1) the descriptive text might not be near the link (either position-wise on the screen for low vision users, or sequential-wise for blind users)
2) the links might be in a table, so if a screen reader user were to list all links on the page, they might get: download statement, download statement, download statement...
3) Offscreen text labels work with Dragon Naturally speaking , but ARIA labels don't