You mean undiscounted regular prices outside sales? Sometimes the publishers do that, yes (GOG can't change prices).
80% is rather rare tho. Can you name an example?

You can track recent price development here: https://www.gogdb.org/

Are you asking whether you get money back retroactively, because the games you bought in the past are cheaper now?

o.O

If I understand the question correctly, then no. You don't go to a store to get some money back because an item you bought three years ago is now heavily discounted, do you?

*flops about tinyE love doll you bought

You weren't supposed to mention that in public!

No I don't think GOG does that.

But if they do, then I too would like a refund of every single dollar more that I ever paid to GOG for any & all games which were subsequently sold for less dollars later on.

Assuming people's interpretation of o.p.'s request is correct...

Has anybody ever asked this about Steam? I have a hard time imagining that. Like, certainly we should hold GOG to a higher standard for DRM-free and maybe technical issues for older games, but sometimes it seems like people expect so much more from GOG compared to Steam when GOG makes like 1% of the money Steam does.

If everybody understood the question correctly the only valid reply would be this.

I'm not positive what's being asked here. Publishers will sometimes lower the base price, discounts tend to grow steadily over time, and GOG regularly updates prices based on currency conversion. I can't think of any other adjustments.

I've never heard of any store offering anything if something you bought becomes cheaper, beyond a short time frame. In this case, there's a 30-day refund policy, provided you haven't played a lot/most of the game (not an issue if you disable time tracking or don't use GOG Galaxy at all).

Consider what the effects would be if a company retroactively gave money back to prior customers every time they put an item on sale.

Let's think through this. Let's say you purchased a new "top tier" game from GOG on its release 5 years ago for $49.99. You have been able to play that game for 5 years now. Hopefully you've enjoyed it! But even if not, you've still received the full "value and benefit" of your purchase since you have had access to that game (and will continue to have access to it forever more thanks to DRM-free distribution) for 5+ years.

But now, the game is "old" (or at least "older"), and GOG is putting it on discount for 80% off ($9.99).

So, you're saying that GOG should refund you $40 for a game that you've been playing and enjoying for 5 years, because... __________

Sorry, but I'm going to need you to fill in that blank.

Yes, they have adjusted. They now offer a whole new range of games for you to purchase at full price.