Except that Nintendo still sells those 20 year old games, so yeah...they are kinda losing revenue.
Wrong. They sell remakes. The average Joe is not going to look for roms and BIOS files (for relevant emulators). The people who do aren't Nintendo customers in the first place. Also, your quote entirely ignores the DMCA exception. Next time, try not quoting from an armchair lawyer.
On the other hand, people who do play these old games will have incentives to buy current Nintendo gear for the latest versions of their games.