Okay for your information pts this is why...
When a person who has the GOG version of the game that was downloaded upon release attempts to install the latest hotfix, the following error message comes up in the GOG downloader...
"This patch does not support your version of the game please download a new installer"
The installer it refers to is the latest 8+Gig installer that GOG has posted in their download section.
So that is why people are complaining. They are not offering as you say "patches for people with older installers" in this case.
The only way to update the latest patch from Larian via GOG is to completely download the whole game again.
I hope that makes more sense.

edit:
and Jacob Marner....I have immediately updated every patch as it has been released by GOG....so that is not the issue.