What is that supposed to mean? Thanks!

Exactly what it says on the tin. This is your last chance to get the games in the promo at a reduced price before they are removed from GoG later this month.

Hm, why would Bohemia remove them anyway? I don't get it.

Me neither.

I can only speculate, but my guess is that with gamespy going away they don't want the massive headache as customers from all online retailers except for Steam would demand refunds for having been sold games with non-functioning multiplayer (which isn't actually true, but the world is crushed under the tyranny of the computer illiterate). It is not just GOG. They are ending their partnerships with ALL retailers except for Steam, and they are changing the titles they are actively providing support for migrate to Steamworks. That is, ArmA 2: Combined Ops, ArmA 3 and the Take On series.

That is my ultra-pragmatic guess, don't mistake it for fact or even a well researched and qualified guess.

I think in a large part that is true, the other part would be Steam providing multiplayer servers on the condition of being Steam only.
It shouldn't be hard to patch a new host server adress into a game.

Shouldn't some anti monopoly/cartel commission step in by now or do we just wait until Steam monopolizes everything?

I considered it, but I am not THAT cynical. The thing about steam though is that it adds a whole new layer of demand in terms of supporting your game. Before the end of gamespy all retailers (including steam) provided the same product more or less. Sure, they released downloadable patches and incorporated those patches into steam roughly at the same time. Now that the games are slated to become much more nestled with Steam, it would require Bohemia to put together at least two different builds of their patches for all their actively supported games, one for the Steam versions and one or more for the de facto obsolete non-steam versions they don't really gain much from supporting.

It is rather simple: The games are going Steamworks in order to function properly, so it is misleading to sell the game through other retailers if the customer have to redeem their purchases on Steam anyways to get a functioning server browser and official patches. This is particularly sensitive when it comes to GOG, which is full of entitled but also largely computer illiterate customers who expect full DRM free functionality out of their games. I think that is irrelevant for a mallable and extremely personalised/moddable product like the ArmA games, but GOGers will always have their soap boxes, practical truth be damned.

Setting up an alternative to gamespy and patching the game accordingly shouldn't be too difficult, but I do not blame Bohemia for not bending over backwards to make it happen when it's easier and possibly less costly to support a steam only title.

I never understood the reasoning behind this, a separate Steam version isn't neccessary only if Steam demands it, sorry I can't see another reason for this.
Also Bohemia is rich enough to host their own multiplayer servers but Steam probably did them a lucrative offer so they basically said to go screw urself if you're not on Steam.

This was true before when gamespy handled the server list, authentication and NAT traversal. With it going away, Bohemia looked at Steamworks and figured this was the fast and easy solution. The ArmA series on Steam was never actually tied to steam in any way before, the build was the same and used gamespy as always.

The way this happened so fast, I'm not saying it is completely unlikely that Bohemia will look at alternatives in the future and that very suddenly going Steam only is a short term solution. Still, the realist in me knows that ArmA 3 is their baby, everything else is a legacy back catalogue that can never be as financially important as their main title. The reality of business is that you can not provide endless fan service just to spread peace and love in the world.