Zeewolf: There's no use trying to portray this as anything else than DRM - that's what it is. Ancient or not.
If the choice is between GOG adding a good old game that has such DRM or not adding it at all, then clearly I prefer the first option and the extra hassle. But if possible, such systems should be removed just like with Waxworks.
Agreed on point 1 fully.
For point 2, there appears to be no available crack for the Ishar series for PC. So, sadly, there's nothing for the GOG team to apply to remedy the situation and I doubt their staff has the expertise to step through the program in a debugger, find the subroutine location that goes to the copy protection scheme, and replace the JMP instruction location with the location a successful code entered goes to.
[url=http://www.csn.ul.ie/~darkstar/assembler/tut3.html]http://www.csn.ul.ie/~darkstar/assembler/tut3.html[/url]
I could probably do it if I had the spare time. I wrote a crack for The Summoning a long time ago. But I'm way too busy these days.
Waltorious: As for GOG removing the copy protection: as others have said, the problem is that it's hard-coded into the game, and can't be changed without access to the source code, which GOG does not have. Other cases like Waxworks are likely exceptions where the rights-holders for the game allowed GOG to make alterations (GOG also includes alterations to Outcast and Thief 1 / Thief 2 / System Shock 2 to get them to work on modern operating systems, and again this was done with express permission from the rights-holders).
Nah, that's just not how it works. People step through the code in something like
good ol' Debug.com in DOS or
Watcom's Debugger and find where the copy protection scheme kicks in and typically apply a JMP patch as I mention above. This is a very standard thing.
http://en.wikipedia.org/wiki/Comparison_of_debuggers