If a file is downloaded from lightworks user and describes a proprietary product - like Benjamin Moore paints for example, it will not work.
It will not work because Archicad can edit all materials and there is currently no way to "lock" a material description. This could lead to you editing the paint color without authorization.
The other rason a(n) .lwa file won't work is that it addresses features not yet implemented, like radiosity and global lighting and some other sophisticated things that don't immediately come to mind.
I suggest that if users are unhappy with the current Arhicad material library that they explore the .lwa files installed with Archicad but not given a material description. These are located with the "Load Material From Archive" button in the material dialog box. But start with a duplicated material because as soon as you find a material in the archive you like, an "OK" over-writes the existing material.
Dwight Atkinson