When you buy something, you buy something, it's yours as a whole, period.
There is no way you can be stripped by small parts of the initial buy.

You don't have to be "expert in law", this is basic common sense, it's like 1+1=2 easy.
Nobody can trash your property right by taking away bits from it. No matter if its physical or digital.
And if there are "laws" that permit these kind of bad practices then those laws are obviously and fundamentally wrong and must be changed ASAP.

Right now, the digital goods market is new, like the old wild wild west where everybody can do almost anything and get away with it. Consumer rights are trashed on a daily basis.
I have no doubt that this will be solved in the future (hopefully sooner than later), it can't go like this. It's preposterous, it's nonsense.
So yea, suing really helps in speeding up the process of implementing/fixing/changing laws in the digital goods market/domain.

On GOG it is.

I'm not sure if it is a decision by GOG what to take away from the customers or whether the rightholders made that decision.

Nope.

Thanks you saving me time searching. ;P

I wasn't talking about GOG removing stuff. Of course that has happened before. I was jut joking about the fact that digital goodies come in limited supplies. Ah well.

For example in employment law there are some things which you could change via work contract and some which you cannot because they are above all (like minimum wage i.e.). The same thing goes for some of the laws in business law. Unfortunately I cannot give you an example which would match this special case because in GOGs case the whole situation is a bit different because of the specific kind of the goods GOG does sell. This is also the problem why I cannot just look into my books and find out if what GOG did is against the law or not. I have a strong feeling that it might be and I want to prevent GOG to get in trouble but entertainment law might work a bit different and may have different clauses of which I don't know. If somebody knows a good lawyer specialized in entertainment law you might ask him and he might help but all I know is that those law works a bit different.

So long the best thing everybody can do is get all those bonus material from GOGs servers to be secure. I really don't like this. Why do I have a shelf if I still have to secure everything?
You are right with this BUT as long as GOG is still in business they have to stay true to their promises. One of them is "download it as often as you like".
As I said before. The rightholders have no say in things which were already GIVEN AWAY! It's true that you only buy the right to use the software but It's not that they were only given for a limited time to the end user or with theright to reclaim those using rights at any time. Would be funny if Bruce Springsteem (or his company) would ring my bell and say to me that they don't like it when I listen to his music and so they are reclaiming the rights to use his music. The more analogies you build the more it is getting clear that this cannot be allowed.

Would I be wrong in assuming that all DosBox games would be Linux-compatible?
Wouldn't, for instance, "Syndicate Plus" run in DosBox? Yet it is not labeled as available in Linux.
Is is because it runs on Window's compatibility mode? But then again, it says that it works on Mac OS X, so it most likely is distributed with DosBox.

What am I missing? Having a label saying the kind of emulation used would make it so much easier for me (and many others, I assume).

It is possible that some link in the complex licensing chain expired, and GOG is at the bottom of it.

However, I do agree with you. Some times I purchase a game because of the extras. I am purchasing the entire package. If GOG pulls something from it, I will feel cheated.

It may be legal it may be illegal and it may be on the edge of it. Fact is if somebody is new to GOG buys a game and get taken away part of the bonus material he might never return to GOG (and in worst case scenario now use STEAM) so GOG should make more obvious that bonus material is under the risk of being taken away (that is if the right holder really can order GOG to pull bonus material already given away). I am downloading my complete bonus material as I write this.

Steam pulls the same crap.
Recently GTA: SA had an update that removed songs from the radio.

Yes, but STEAM is known for making its own laws. I always thought that GOG is different and I still want to believe this.

BTW: The GTA situation really sounds like the devs never had the rights to include those songs and so they tried to prevent damage by pulling those songs. Still not correct but as I said: it is STEAM (I remember how I had to fight to get my stolen account from them back once - since then I am only buying there if I have the possibility to play it without STEAM and it don't have the possibility to get the same on GOG).

Sounds more like the license on those specific songs ran out. :P
Still ridiculous that changing it is even allowed.

I guess there is no risk of losing the WItcher Bonus material (>4GB) because of CD-Project RED and GOG being the same?

As usual, it is very possible to run DOSBox games in Mac/Linux, even when it's not mentioned in the game's page. Why is it not mentioned, you might ask? Two reasons:

1) Mentioned OSs means that should the game not work correctly in the depicted OS, you are guaranteed GOG support to help you troubleshoot the game. No such help if you try to run a game on a non-officially supported OS. Yes, even if it's just DOSBox. This is easily explained by...
2) ...deals with the license holder. They can make or break what versions may GOG officially distribute and support. For instance, GOG could easily add a DOSBox version of Dark Forces for Mac, but since there was an earlier Mac port by a different distributor, they aren't legally able to do so.