The download version is not a patch of the disk version.
Exactly how much do you think they are making off the GOG/Impulse version?
Now, how much do you think it would cost to develop and test a patch against all previous game/save versions? How much do think it would cost to hire companies to localize the updated version, and beta test patches for other language versions? (unless of course English speaking people are the only ones who deserve free updates in perpetuity)
I guarantee the original publishers are not going to pony up any money or resources to put out another patch.
