The "L" part was an effort to include all the speakers of Romance languages who say "software libre" or "software livre". In my experience living in South America, very few people say "código abierto" or "fuente abierto" at the Linux conferences except if they are companies presenting business plans. For most, they don't see the need for the division between "free software" and "open source", so FLOSS is a more inclusive term to cover more of the world.

My personal belief is that we need the discourse of both the OSI and FSF because they appeal to different segments, and we need both the business community and people care about user rights to be in the movement if we want FOSS to succeed.