I don't see why so many people insist on being able to downgrade CK2...
Fundamentally, this is an issue of freedom. It is, simply put,
stupid to not be able to access old versions--there is no real downside to it, because the patches can be hosted elsewhere. (As many of the CKII patches are.) With an automatic patching system like Steam has, or a system where you can only download the latest version when you buy it new, you are actually increasing the workload because you have to expend more time and bandwith providing the latest patch rather than letting users do this themselves. Not allowing access to previous patches is almost bureaucratic.
There are practical sides to it, too. If you want to play mods that are not compatible with the most recent version (i.e. every major overhaul, when a patch has just been released) or the newest patch introduces major bugs, it can be very useful to play older versions. You shouldn't have to hoard old version copies of your game files or resort to downloading the game from less-than-reputable sources to do a simple thing like that.
Let me spin you the tragic tale of an old game called Aquanox. Patch 1.19, the last it would see, introduced a bug that literally made it impossible to complete the game. Had Aquanox been one of those games of which you could only download the latest version, and which was automatically patched, the only people who would've been able to complete it were those who had hoarded their old versions. (Or pirates, because whenever software gets more restrictive, it seems legitimate consumers lose out and pirates get the restriction-free version anyway.) Luckily, Aquanox is from the good old days of CDs and manual patching, so you could just install the base game and patch it up to the non-broken patch you wanted.
