The build used by Redguard is from 25th July 2013, while the latest version is from January 2015, with significant improvements.

Is there any real reason for this?

One is tested and works, the other is untested and may or may not work? And is it the 2013 build or a branch based on that one?

Probably testing, if they update for one game they'd have to test and update for all the other games eventually. My guess is that they won't update until this Galaxy business is over or they find a significant game that won't run with the older version.

Plus, it's possible for people to do their own update, even if it is a bit of work.

Are any of these "significant improvements" actually significant to running Redguard? Personally I'm using the January build when running non-GOG DOS games but a look at the changelog doesn't reveal any fundamental changes that users will actually notice.

The improvements are really quite significant, for example, the newest version runs the game with texture filtering and properly emulated lighting. As you can imagine, the image quality is a lot better, while, I admit, the performance is somewhat worse, but still acceptable.

That's probably your answer right there. GOG is quite conservative with the software it uses. Plus, they are short on time these days. For instance, some DOSBox bundled games here are still running on version 0.73.

Here is a screenshot for those interested:

http://www.mujweb.cz/nakamura/gfx/redguard.jpg

I think you just answered your own question. "Still acceptable" is a subjective term. Just because it is acceptable to you does not mean it is acceptable to everyone. And GOG needs to make their releases acceptable to the broadest segment possible.

Given how easy it is to switch out the DOSBox version of the game, I suggest you just do that.

Speaking of, games that read music from a disc image (like Blood for example) have working CD music volume sliders in SVN-Daum builds. I wonder why GOG doesn't include those instead by default since the music can be jarringly loud unless you tweak it in the conf files.

This reminds me, didn't they set it up so that it would use a normally installed copy of DOS Box instead of the bundled one if you've got it installed?

I'll have to look into it, because that was quite a while ago. It was about the time they started using that newer version of DOS Box for some of the games.

I don't think so. I believe the old installers offered you the option to manually choose an existing DOSBox installation during the installation of the game, but I'm not sure the new ones do, and I'm quite certain none of them ever did it automatically.

I looked into it and you're right, there used to be an option to do that, but I haven't seen that option any time recently. It was probably removed when they did the 2.x installers.

There's a bluetext comment on http://www.gog.com/wishlist/site/update_dosbox_and_scummvm_games_to_latest_versions about why GOG doesn't update its existing installers. (Owing to what I presume was a glitched spam removal, it's attributed to ##@@##@@.) I don't know of any similar comments about fresh releases.