hmcpretender: Depends on what you mean by "broken". If the games doesn't start or crashes constantly I obviously would not play it and it shouldn't be published to begin with.
MarkoH01: Especially with small indie games (devs justz don't have enough time/money/manpower to test for everything) it's not uncertain that a certain game cannot be completed at all or that the game has other bugs. So while the devs fix those issues on Steam because it is the store they focused on during development the game remains broken on GOG. Remember: updates are rarely additional features but more often than not bugfixes.
Well, GoG would be well advised not to include games of questionable quality in their catalogue. The vague possibility of future patches shouldn't be play a role in that descision. If something broken still slips in, then refunds are probaly in order.
This however shouldn't stop GoG to make buisiness with trustworthy developers and bring their games here, even if they are younger than 5 years and still receive patches...