There still exist game platforms that provide offline downloadable game installs. GOG.com is one example. I know this is but one example but I think it's important people reward this behavior so companies know there is demand for this.
Edit: according to this post on the forum the feature is not maintained or supported (as of 2016).
https://www.gog.com/forum/the_witcher_3_wild_hunt/how_can_i_...
But Galaxy is optional, you can download the offline installers directly from the site. I have around 680 games on GOG and all of them are in my external HDD in their offline installers - i never installed Galaxy on my PC.
Its selection is small but it has a few exclusives - Alien Trilogy was released recently-ish there. Also they're the only place where you can find the original Duke Nukem 3D with all of its expansions due to some perpetual contracts they had with 3D Realms before the IP was acquired by Gearbox.