In Unity the "Launcher" can have any application pinned to it even if said application does not have a .desktop file, I assume that if it detects an application does not have one it just creates one for it in its own area for itself (the Launcher) to use. The GNOME dock however does not have such functionality, and though I understand that it's very simple, to pin an application to the dock all you have to do is make sure that that application (as with most dock applications) has a .desktop file, and if it does not then you have to make one for it. However most end-users will probably not know anything about .desktop files and even if they do, may not want to create one for every program which doesn't have them, and a lot of program especially ones compiled by the user from source don't have .desktop files with them, or even ones from sh installers from the internet that don't come from the repositories often don't have .desktop files.

So I think that the GNOME dock (in the Activities Overview) would greatly benefit from such functionality.

I initially proposed this functionality here but thought I should also do so upstream: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1586839