Yes I do, but I try to be cautious about it.

I rarely buy anything on the release day anyway, one reason being the higher prices, and another if I see or realize the game will have DLCs later (I prefer to wait for a "gold edition" which includes all the small parts).

To me that fact that a GOG version gets an update or DLC later than the Steam version is not a big problem in itself... as long as they come. Of course if it is routinely several months or a year after the Steam update, then it is not ok anymore.

Also, it depends to me what exactly is missing. For example:

1. "The GOG version is missing the German or Cambodian language version of the game!". Sorry, I just can't give a shit because I don't wish to play any of my games in German or Cambodian. I only want the English versions, thank you. Even for Finnish games, I don't really look for Finnish language versions (e.g. the Trine games?).

Sucks for those who want non-English versions though, but I am not going to boycott games for something I don't personally need.

2. "Missing Linux and/or Mac versions!". I don't play on Mac, so meh. For Linux...hmm a native Linux version would be nice just in case, but if the Windows version is the primary version of the game, I'm fine with that too. I can use a Wine wrapper myself if I get an urge to play my games on Linux.

3. "GOG version is missing the multiplayer", so what else is new? As long as I am aware what the GOG version is missing so that I can make my own decision if it is ok to me. I don't need multiplayer part for games where I'd play the single-player part only anyway. Team Fortress 2 fulfills my online multiplayer gaming needs at the moment, I buy GOG games for their single-player parts.

Like Brutal Legend, when I bought it on GOG I knew already it is missing the multiplayer component... and I was fully fine with that myself. I knew I'd probably never play the multiplayer part anyway.

As explained above, I am not going to boycott some game for something that doesn't really affect me. If it affects me, then yes. For instance, if the publisher of Slender: Arrival would release something else here, I would be very cautious to buy anything from them.

For that purpose fronzelneekburm has done great work, keeping up a list of games which are missing something. Then I can check whether it affects me or not, and make a conscious decision whether to buy the game or not.

On the other hand, I don't want to reward such publishers either (who bring a game to GOG but abandon it), by e.g. buying the game from Steam, unless it is a game that I feel I have to have (Slender is not one). In such cases I might just opt not to buy the game at all.

How should they have planned it then, ie. what should they do differently? The wishlist item is vague about that, just demanding that all games on GOG should be up to date (how exactly to make that happen?), and something about a contract demanding them to be up to date (which is not quite as simple as the wishlist item suggests).

In a way I guess I am already doing what you propose, ie. hardly ever buying GOG games on release, but waiting some time until they are not receiving more DLCs (and are not that actively updated anymore). But I quite often eventually buy them anyway, unless I recognize they are missing something that affects me sorely.

For instance that Armello game, most probably I will not buy it (not on GOG, nor on Steam) if the publisher has really decided not to bring e.g. some single-player DLCs to the GOG version. Their loss, no money from me.