The "All" channel was removed from the old MA (now the LW arenas) due to numerous complaints of the inane banter on it. The decision at the time was to create a channel (200 was chosen) that players may choose to read if they wanted but was still moderated like the original "All" channel.
Personally I like the idea better than being able to squelch the "All" channel, as salutes are still available, and it could be a civil means of communication. I believe this was only implemented in the LW arenas as they are the most used, and most prone to text abuse, but that's just my guess.