Well, the problem is that new CD-keys for Warband do not work with older versions anymore. This must be a new problem, and I think TaleWorlds is to blame for the lack of support. This makes new people unable to play the mods that require an older version (and there are plenty of excellent old mods that haven't been updated). In the case of Víkingr and The Deluge, the reason for using an old version of Warband was that the post-Napoleonic Wars patches didn't bring anything significant to base Warband and most importantly that the version of WSE available for the Víkingr (and The Deluge) development team ceased to be updated. All in all I think the stand-alone solution was rather ingenuous, and has been preferable by far to an updated non-WSE mod. Recently we've discovered some flaws in WSE that made the mod susceptible to hackers, and with this recent development barring new players from activating the Víkingr stand-alone, we have come to a point where it feel necessary to look into releasing a version that is compatible with the newest Warband version - even though this will probably lead to loss of some of our lovely features, not to mention the fact that the post-Warband 1.143 .exe still doesn't accept special character (not even relevant letters such as Þ, ð, ö, etc. which might have been expected after the Viking Conquest release), meaning that anyone with a hex-edited name will be automatically banned on all servers.
On another note, I would personally be very angry with the way TaleWorlds has handled this. Of course CD-keys should be valid no matter what version you are using!