Yep, sorry… I mixed up the two. 
But basically, .riff files (as well as .aiff ones) are compatible with .wav as both share the common IFF (Interchange File Format) structure defined 30 years ago.
https://en.wikipedia.org/wiki/Resource_Interchange_File_Format
https://en.wikipedia.org/wiki/AIFF
After this, I indeed wonder why there is such an automatic conversion in luke7020 case…