I have the same problem. I did the steam --reset trick, but the problem is still here. I made a list, so maybe you can see a pattern?
Games that show the default icon (https://framapic.org/mkSzwKCwl1f4/V2tnEyrP):
Games that show the binary icon (https://framapic.org/N3MOpDBmlGqN/WJ87p5ha):
Games that show the right icon:
Edit: I'm not using the supported configuration, but since it's about .desktop files, which are pretty standard now, I assume it's the same with Ubuntu. I have Fedora 22 with GNOME 3 (vanilla).
Dupe of #989. As explained there, this is an issue with the games and should be reported as such to each individual game's developer.
Ok, I guess we can close this one then
@Plagman posted at https://github.com/ValveSoftware/steam-for-linux/issues/989#issuecomment-394548865: "Yes, the problem was that we didn't have .pngs to put in there because the developer never specified Linux icon files, only a Windows icon. The next Beta will include a systemic fix for this that will let the Linux client fall back to Windows icons and convert them appropriately; games will have to be reinstalled and the shortcuts recreated for the proper icon to get redownloaded, unfortunately."
Some games use the generic steam icon instead of their own as seen here: http://i.imgur.com/mdqgzF3.png
This is annoying enough on the desktop, but it becomes more of a problem when you're having icons added to the application menu and it's hard to distinguish games from each other.
If some of the games' developers aren't contributing icons for this use, can't steam use the icon it uses for each game in the library view? (as seen here http://i.imgur.com/QIS4jmc.png ) It might look poor depending on how large those icon files are, but it would still help for the menu's where icons are small anyway.