The Dash will search through your .desktop files and use the name provided and comments so that you don't have to enter "Firefox", for instance. Entering "web" will do just as fine, since "web" is part of the description of Firefox.
In the case of LÖVE, the application developer has specifically asked that the application should not show up in menus by specifying NoDisplay=True in the desktop file. I don't know exactly why they've done this, but it might be because it requires a filename input in order to do anything useful.
If you think this should be different, you can file a bug with the LÖVE developers by pressing Alt+F2 and enter